IRDAS-Report ALPSGuideDocumentation Mar2010 · ESA-IRDAS – ALPS User Guide and Documentation Differential Absorption Spectroscopy in the SWIR for GHG Monito ring using Coherent

Wegener Center for Climate and Global Change University of Graz Leechgasse 25, A-8010 Graz, Austria

ARSCliSys Research Group ESA-IRDAS Project Report

WEGC Technical Report for ESA-ESTEC No. 3/2010

ESA-ESTEC study

IRDAS – Differential Absorption Spectroscopy in the SWIR for Greenhouse Gas Monitoring using Coherent Signal Sources in a Limb Sounding Geometry ESTEC Contract No. 21759/08/NL/CT–September 2008

WP5 Report

ALPS ACCURATE LIO Performance Simulator

User Guide and Documentation

G. Kirchengast, S. Schweitzer, and V. Proschek Wegener Center for Climate and Global Change, University of Graz (WEGC), Graz, Austria

G. González Abad, G. Li, N. Allen, J. Harrison, B. Thomas, and P. Bernath Department of Chemistry, University of York (UoY), Heslington, York, UK

March 2010

ESA-IRDAS – ALPS User Guide and Documentation Differential Absorption Spectroscopy in the SWIR for GHG Monitoring using Coherent Signal Sources in Limb Geometry (ESA C.No. 21759/08/NL/CT)

Study Partners: UoY UK • WEGC Austria • DMI Denmark ALPS Contact: [email protected], [email protected], www.wegcenter.at

Page ii of viii

(intentionally left blank/back-page if double-sided print)



Page iii of viii

Table of Contents

List of Acronyms ...................................................................................................................... v

List of Constants.....................................................................................................................vii

PART 1: ALPS Overview and User Guide ............................................................................ 1

1 Overview............................................................................................................................. 1 1.1 Structure of the ALPS Software ............................................................................................... 1 1.2 ALPS Control File and Main Program ..................................................................................... 3

2 Setup and Use..................................................................................................................... 6

PART 2: ALPS Documentation – Routines and File Formats............................................. 7

1 I/O Routines including RFM Atmosphere and Transmission Profiles Ingestion........ 7 1.1 PRO IO_RFMAtmosandTransmProfiles .................................................................................. 7 1.2 PRO IO_AtmosLossGainProfiles ............................................................................................. 9 1.3 PRO IO_ObsSystemandSNRProfiles ..................................................................................... 11 1.4 PRO IO_ObsSystemErrorProfiles .......................................................................................... 13 1.5 PRO IO_RetrievalErrorProfiles .............................................................................................. 15

2 Atmospheric Loss/Gain Modeling Routines.................................................................. 19 2.1 PRO AtmosLossGainModeling (envelope routine)................................................................ 19 2.2 PRO DefocusingLoss.............................................................................................................. 24 2.3 PRO RayleighScatteringLoss ................................................................................................. 27 2.4 PRO RayleighScatteredSolarRadGain.................................................................................... 29 2.5 PRO AerosolExtinctionLoss................................................................................................... 31 2.6 PRO CloudsExtinctionLoss .................................................................................................... 33

3 Atmospheric Error Modeling Routines......................................................................... 37

4 Observation System and SNR Modeling Routines ....................................................... 39 4.1 PRO ObsSystemandSNRModeling (envelope routine) .......................................................... 39 4.2 PRO LinkBudgetModeling ..................................................................................................... 41 4.3 PRO AvailableSNRModeling................................................................................................. 45

5 Observation System Error Modeling Routines............................................................. 47 5.1 PRO ObsSystemErrorModeling (envelope routine) ............................................................... 47 5.2 PRO TxErrorModeling ........................................................................................................... 49 5.3 PRO RxErrorModeling ........................................................................................................... 50 5.4 PRO ScintErrorModeling ....................................................................................................... 52 5.5 PRO TotalNoiseModeling ...................................................................................................... 53

6 Retrieval Error Modeling Routines ............................................................................... 55 6.1 PROs RetrievalErrorModeling................................................................................................ 55 6.2 DiffTransmissionRetrievalErrorModeling.............................................................................. 58 6.3 TraceSpeciesRetrievalErrorModeling..................................................................................... 59 6.4 PRO losWindRetrievalErrorModeling.................................................................................... 61

7 ALPS Plot Utility ............................................................................................................. 68 7.1 PRO alpsPlot........................................................................................................................... 68



Page iv of viii

8 File Format Descriptions................................................................................................. 69 8.1 RFM Atmosphere and Transmission Profiles Data File ......................................................... 69 8.2 Atmospheric Loss/Gain Profiles Data File ............................................................................. 70 8.3 Observation System and SNR Profiles Data File ................................................................... 72 8.4 Observation System Error Profiles Data File.......................................................................... 74 8.5 Retrieval Error Profiles Data File ........................................................................................... 76

9 References......................................................................................................................... 79



Page v of viii

List of Acronyms ACCURATE (Atmospheric Climate and Chemistry in the UTLS Region and climate Trends

Explorer; now used as a generic proper name for the LMIO mission concept) — climate benchmark profiling of greenhouse gases and thermodynamic variables and wind from space

ARSCliSys Atmospheric Remote Sensing and Climate System (Research Group of WEGC) ALGM Atmospheric Loss/Gain Modeling ALPS ACCURATE LIO Performance Simulator APD Avalanche Photodiode DCT Design Control Table DFB Distributed Feedback EGOPS End-to-end Generic Occultation Performance Simulation and Processing System ESA European Space Agency FASCODE FASt Atmospheric Signature CODE FSD Free Space Distance FSL Free Space Loss HITRAN High-resolution Transmission molecular absorption database IDL Interactive Data Language (programming language) IR Infrared IWC Ice Water Content (of clouds) LEO Low Earth Orbit (satellite/s) LIO LEO-LEO Infrared Laser Occultation LMO LEO-LEO Microwave Occultation LMIO LEO-LEO Microwave and Infrared Laser Occultation (combined LMO and LIO) LWC Liquid Water Content (of clouds) NoP Number of channel pairs that are evaluated in ALPS calculations NEP Noise Equivalent Power NP Number of parameters (which is number of channels plus number of transmission

derivatives) oI, I optional Input, Input oO, O optional Output, Output OSEM Observation System Error Modeling OSSM Observation System and SNR Modeling RATP RFM Atmosphere and Transmission Profiles REM Retrieval Error Modeling RFM Reference Forward Model RMS(E), rms(e) Root-Mean-Square (Error) SNR Signal to Noise TIA Transimpedance Amplifier TOA Top of atmosphere TP Tangent Point (or tangent point location) WC (Number of) wind channels (equals 2) WEGC/ Wegener Center for Climate and Global Change, UniGraz University of Graz (Austria) UoY University of York (UK) WP Work Package



Page vi of viii

(intentionally left blank; back page if double-sided print)



Page vii of viii

List of Constants c1 23.7104 [K/hPa] Constant in Modified-Edlen refractivity formula c2 6839.34 [K/hPa] Constant in Modified-Edlen refractivity formula c3 45.473 [K/hPa] Constant in Modified-Edlen refractivity formula clight 299792458 [m/s] Velocity of light (in vacuum) d1 130 [1] Constant in Modified-Edlen refractivity formula d2 38.9 [1] Constant in Modified-Edlen refractivity formula e1 0.038 [hPa-1] Constant in Modified-Edlen refractivity formula fn 1.25·10-29 [m3] Factor in simple air density profile formulation g0 9.80665 [m/s2] Gravitational acceleration h 6.62607·10-34 [Js] Planck constant kB 1.38065·10-23 [J/K] Boltzmann constant Mair 28.964 [kg/kmol] Mass of the dry air n0 2.5·1025 [m-3] Air density at the surface (for simple formula) Rd 287.06 [J/kg/K] Specific gas constant for dry air RE 6371.0 [km] Radius of Earth (spherical Earth) Rgas 8314.5 [J/K/kmol] Universal gas constant Rw 461.52 [J/kg/K] Specific gas constant for water vapor Ssun,1AU 1368 [W/m2] Solar constant (at 1 astronomical unit) Tsun 5900 [K] Surface temperature of the sun Composed/derived constants:

aw = Rd / Rw = 0.62199 (0.622) moist air gas constant ratio bw = 1 – aw = 0.37801 (0.378) complementary constant to aw cl1 = 2 · h · clight2 = 1.1910·1020 [Wm-2nm4sr-1] 1st Planck radiation constant cl2 = h · clight / kB = 1.4388·107 [nmK] 2nd Planck radiation constant σ = (2 · π5 · kB4) / (15 · clight2 · h3) = 5.6704·10-8 [Wm-2K-4] Stefan Boltzmann constant



Page viii of viii

(intentionally left blank; back page if double-sided print)



Page 1 of 79

PART 1: ALPS Overview and User Guide ALPS (ACCURATE LIO Performance Simulator) is a small, self-contained software package written in IDL (Interactive data language). It is developed under lead of the Wegener Center for Climate and Global Chang, University of Graz (WEGC), Graz, Austria. Current develop-ers are WEGC and the Department of Chemistry of the University of York (UoY), York, UK. This document provides information on the functionality of ALPS and user guidelines (PART 1) as well as a documentation of routines and file formats (PART 2). 1 Overview ALPS enables simplified LIO (LEO-LEO Infrared-laser Occultation) end-to-end performance estimations under different atmospheric conditions. In particular, LIO trace species retrieval errors and wind retrieval errors can be estimated under consideration of various atmospheric losses/gains and observing system/instrumental errors. The estimations are based on limb transmission profiles, influenced by atmospheric absorption, that are computed using the Ref-erence Forward Model (RFM; RFM, 1996 & 2008) that is mainly developed by A. Dudhia at the University of Oxford. RFM is operated using the HITRAN molecular spectroscopic data-base (HITRAN, 2005 & 2009) and FASCODE standard atmospheres (FASCODE, 1986). 1.1 Structure of the ALPS Software Figure 1 below shows the structure of ALPS in a schematic block diagram. All main building blocks (IDL envelope routines) are visible and the modules (IDL basic routines) which belong to those blocks. In addition, the input/output routines that create the ALPS data files (write mode) or read them for use by subsequent routines (read mode; e.g., used by the plot utilities) are depicted. The data files themselves (ALPS “Profiles Data” files) are shown as elliptically-shaped elements.

The ingestion chain from the Reference Forward Model RFM (backed by the HITRAN-2004 resp. HITRAN-2008 database and the FASCODE atmospheres; for details on RFM and ac-cess to FASCODE atmospheres, incl. US std. atmosphere, see www-atm.physics.ox.ac.uk/ RFM, for details on HITRAN-2004 www.harvard.edu/HITRAN) is visible in the upper right of Figure 1. RFM is to be acquired from Univ. of Oxford (A. Dudhia, see the above RFM web link) and is to be run as a pre-process, driven by its own control file, to prepare the RFM at-mosphere and transmission profile (RATP) data for ALPS. These RFM-derived RATP files are the interface from which ALPS ingests the atmospheric and transmission profile data.

ALPS as a whole is steered by a single control file that provides — ordered in logical groups and the parameters specified in a simple Parameter = Value [Unit] format in each group — all specifications needed to execute a given ALPS Task. “Task” is in the ALPS context the user-defined identifier (string variable Task-id, max. 25 characters suggested but no technical limit) that ensures, in a meaningful and effective way, an orderly naming of files from multi-ple executions (each execution belonging to a specific task). The ALPS Main Program reads such a control file and executes it according to the specifications within.

For convenient and quick access to the documentation of each ALPS element, Figure 1 also provides the subsection no. of its description in PART 2: ALPS Documentation.



Page 2 of 79

Figure 1: Schematic view of the ALPS software system. For each module/routine and data file, the corresponding subsection no. in Part 2 where it is described is indicated for convenient tracking. File system structure behind the software structure and naming conventions. The ALPS main program (alps.pro) resides in the ALPS /src/base directory, together with a readme file that basically explains how to run it (alps.README) and some other ba-sic routines. The routines of the sections 1 to 6 of Part 2 reside in the subdirectories /IO (I/O Routines), /ALGM (Atmospheric Loss/Gain Modeling Routines), /OSSM (Observation Sys-tem and SNR Modeling Routines), /OSEM (Observation System Error Modeling Routines), and /REM (Retrieval Error Modeling Routines) of the /src directory, respectively. The Plot Utility (section 7) resides in /src/util.

The .pro filename of each routine is identical to the IDL procedure name, or a short-form name so close to it that any ambiguity is avoided. These procedure names are at the same time used as subsection title for each routine’s description in Part 2.

The data are stored under the /data directory, with the input data under /runControl (ALPS control files) and /RFMin (RFM atmosphere and transmission input data) subdirecto-ries, where the control files shall follow the filename convention alps_.rcf. The ALPS RFM input data follow no mandatory naming convention, their filename is one of



Page 3 of 79

the parameters specified in the control file. However, the example files included suggest a useful naming convention: it is the one from RFM2ALPS-AtmTranProfileData.pro, the program in /src/util used (by experts) for generating the ALPS RFM input files in netCDF format (see section 8.1; *_RATP.nc files). The output data from ALPS runs are stored in netCDF format as well. The output files of in-dividual tasks (four data files per task, examples section 8.2-8.5) follow a filename conven-tion _.nc, with one of ALGP (Atmospheric Loss/Gain Pro-files data), OSSP (Observation System and SNR Profiles data), OSEP (Observation System Error Profiles data), and REP (Retrieval Error Profiles data), respectively.

The Plot Utility (section 7) is an interactive program and the output data are either directly shown on screen or stored as .ps/.eps files in the same subdirectories as the respective output data, following a filename convention -., where . is one of .ps and .eps, respectively. (Note: approach with files is a future implementation plan, currently the utility is implemented for on-screen plots only) 1.2 ALPS Control File and Main Program The run control file (.rcf file) resides in the /data/runControl directory and includes all information needed by the main program. Via this run control file, you can

• select a Task-Id and Creation stamp (version only to change by experts) (see [Gen-eral Identifiers])

• select which data shall be computed (see [General Settings]) • define which RFM atmosphere and transmission data files you want to use for input

(see [RFM Atm Tran Data Input Settings]) • select the pairs of channels you want to investigate (see [Pairs of Channels to

be investigated]) • select the models and settings that are used in the atmospheric loss/gain modeling

(see [Atmospheric Loss/Gain Modeling Settings]) • select the settings for the observation system and SNR modeling (see [Observation

System and SNR Modeling Settings]) • select the settings for the observation system error modeling (see [Observation

System Error Modeling Settings]) • select the settings for the retrieval error modeling (see [Retrieval Error Modeling

Settings]) As a complete listing of such an .rcf file see the example below.

[General Identifiers] ALPS Version = r35 ALPS Task-Id = Test1 Creation Date and Time = 2010-03-15 18:05:00 [General Settings] Compute ALGP Data = yes Compute OSSP Data = yes Compute OSEP Data = yes Compute REP Data = yes [RFM Atm Tran Data Input Settings]



Page 4 of 79

RFM Atm Tran Data directory = ../../data/RFMin/ TargetSpeciesTable File = FASCODEtro_TargetSpeciesTransmission_RATP.nc TotalTransmTable File = FASCODEtro_TotalTransmission_RATP.nc [Pairs of Channels to be investigated] Number of Pairs = 19 No of Pairs regarding WindRet = 1 Pair1 = H2O-1 Ref-3 Pair2 = H2O-2 Ref-6 Pair3 = H2O-3 Ref-5 Pair4 = H2O-4 Ref-5 Pair5 = CO2 Ref-6 Pair6 = CO2 Ref-6 Pair7 = CO2 Ref-6 Pair8 = CH4 Ref-4 Pair9 = N2O Ref-5 Pair10 = O3 Ref-1 Pair11 = CO Ref-4 Pair12 = HDO Ref-3 Pair13 = H218O Ref-2 Pair14 = 13CO2 Ref-5 Pair15 = C18OO Ref-6 Pair16 = 13CO2-2 Ref-6 Pair17 = C18OOw1 Ref-6 Pair18 = C18OOw2 Ref-6 Pair19 = C18OOw1_d C18OOw2_d [Atmospheric Loss/Gain Modeling Settings] ALGP Data directory = ../../data/ALGP/ Defocusing Loss Model Mode = p,T,q Atm Rayleigh Scattering Mode = p,T,q Atm Compute RaylScatSolarRadGain = yes Aerosol Model Mode = SAGE II based Aerosol Load = background Angstroem Exponent = 1.5d0 ;[1] Compute CloudsExtinctionLoss = yes [Observation System and SNR Modeling Settings] OSSP Data directory = ../../data/OSSP/ Tx Orbit Height = 800d0 ;[km] Rx Orbit Height = 650d0 ;[km] Tx Laser Pulse Power = -25.5d0 ;[dBW] Tx Optics Loss = 3d0 ;[dB] Tx Antenna Diameter = 135d0 ;[mm] Tx Pointing Loss = 0.4d0 ;[dB] Rx Antenna Diameter = 135d0 ;[mm] Rx Optics Loss = 4d0 ;[dB] Raw Sampling Rate = 50d0 ;[Hz] SNR Mode = set at TOA Raw Sampling SNR at TOA = 27d0 ;[dB] [Observation System Error Modeling Settings] OSEP Data directory = ../../data/OSEP/ Tx Laser Fluctuation = -30d0 ;[dB] Turbulence Scintillation Mode = medium Scint [Retrieval Error Modeling Settings] REP Data directory = ../../data/REP/ Compute Composite Profiles = yes Composite Profile Species = H2O



Page 5 of 79

Compute Wind Retrieval Errors = yes Wind Model Mode = zero wind Wind Channels to use = C18OOw1 C18OOw2 [* EOF *]

The main program alps.pro needs the name of the run control file as input (as the run-alps script in /src/base shows). The complete content of this file is then read into an IDL structure variable by rcfStruct.pro, making ALPS-internal transmission of the in-put information to any routines simple and straightforward. Afterwards, the main routine steers reading of the RFM atmosphere and transmission data files and calls sequentially the modeling systems. The overall program flow is as follows.

Read run control file input data ↓

Read RFM atmosphere and transmission profiles input data ↓

Call ALGM main routine ↓

Call OSSM main routine and within this OSEM main routine ↓

Call REM transmission and trace species retrieval error routine ↓

Call REM composite profiles estimation (for H2O) routine ↓

Call REM wind retrieval error routine ↓

Write ALGP, OSSP, OSEP, REP output data



Page 6 of 79

2 Setup and Use The ALPS software package can be obtained from the WEGC Graz ([email protected]). You must uncompress the ALPS_r-.tar.gz file (or, with equivalent content, the ALPS_r-.zip file if you got it in this archive format) on a machine that has the IDL software installed (preferably under a Unix or Linux operating sys-tem). You will then have access to the ALPS directory structure including full code and ex-ample data files. This documentation was written to be compliant with the version ALPS_r35, the version by the end of the IRDAS study, but will remain essentially valid also for any small updates afterwards (should you have received a .tar.gz or .zip version higher than r35). Any significant future updates will imply you get an update of this documentation as well. Before running the program you must adapt the run control file (.rcf) in the directory /data/runControl and ensure that the files containing the RFM atmosphere and trans-mission profiles (needed as input; specified in the run control file) are available in the /data/RFMin directory (see section 1.1 above for a description of the file structure). To run the program, switch to the /src/base directory and start IDL. Use a command as follows at the IDL prompt:

@run-alps

This command executes the run-alps file, which is an IDL batch file steering that all parts of ALPS needed for executing the program are compiled and that the main program (alps.pro) is executed afterwards. In the last line of this file, the run control file in use must be specified as input parameter to the alps.pro; default is the alps.rcf file. Typically, two modes are used for running ALPS: Mode 1 - Overriding inputs settings each run To run individual ALPS tasks *while overriding your settings in alps.rcf each run* you may just change the "ALPS Task-Id" in the "[General Identifiers]" section of the alps.rcf for each new run and then execute @run-alps. The output files will not be overwritten since their filenames contain the "ALPS Task-Id" as their prefix (e.g., output files from Task-Id "Test1" will have names starting with "Test1_"; cf. section 1.1 above). Mode 2 - Archiving inputs settings of each run To run individual ALPS tasks *while archiving your settings of each run* you may create derivatives of alps.rcf and run-alps in that you

1. modify the filenames to alps_.rcf and run-alps_ 2. specify your individual settings in alps_.rcf 3. change the last line of run-alps_ to

alps, '../../data/runControl/alps_.rcf' Then execute using @run-alps_. The output filenames are as for Mode 1, i.e., the Task-Id is used as prefix.



Page 7 of 79

PART 2: ALPS Documentation – Routines and File Formats This part includes descriptions of all routines and data files contained in the ALPS software package. The section structure is thereby organized module by module and the modules are grouped thematically, as shown in the ALPS software structure in Figure 1. In particular, sec-tion 1 describes all I/O routines, chapter 2 the atmospheric loss and gain modeling (ALGM) routines, section 3 the atmospheric error modeling routines (currently not in use, functionality shifted to section 5), section 4 the observation system and SNR modeling (OSSM) routines, section 5 the observation system error modeling (OSEM) routines, section 6 the retrieval error modeling (REM) routines, section 7 the data visualization routines and section 8 the file for-mats of ALPS input and output files. 1 I/O Routines including RFM Atmosphere and Transmission

Profiles Ingestion The I/O routines are stored in the /src/base/IO directory of the ALPS software. Gener-ally, there exist separate writing routines for each thematic complex (ALGM, OSSM, OSEM, REM) of the software. These are sequentially described below (sections 1.2 to 1.5). Section 1.1 describes the routine that reads the RFM atmosphere and transmission profile files, that are needed as input to ALPS. Since all data used in ALPS are stored in netCDF file format, a generic netCDF reading rou-tine is used for reading all data. This routine is named netcdf_read.pro and is stored in src/base/IO. The netcdf_read.pro was provided by A. von Engeln (EUMETSAT Darmstadt, Germany, pers. communications, 2009). 1.1 PRO IO_RFMAtmosandTransmProfiles The routine is named IO_RFM_ATP (in io_RFM_ATP.pro), the ALPS routine for reading the files generated with RFM2ALPS-AtmTranProfileData. These ALPS input files (“_RATP.nc files”) contain the atmosphere and transmission profiles obtained from the RFM model in ALPS-compliant netCDF format. General attributes and variables for these files are summarized below. General attributes:

Kind of transmission Laser FWHM Atmospheric file

Variables: Wavenumbers Derivative_Wavenumbers Height Temperature Humi



Page 8 of 79

Pressure Channel_ids Derivative_ids RFM_Channel_Trans FD_Wind

1.1.1 Interface Description Name Type Dim I/O Unit Explanation rcfData STRUCT I Run control file structure DirRFMinData STR scalar I - Folder with RFM files TargSpecTrTab STR scalar I - File name of the RFM Target Species

transmission profiles TotalTrTab NoOfPairs

STR INT

scalar scalar

I I

- -

File name of the RFM total transmis-sion profiles Number of channel pairs to be inves-tigated

traTdata STRUCT IO Transmission profiles structure KindofTran FwhmLaser AtmFile NoOfHeights NoOfParams NoOfNoTran Param AtmRegion NWindDerivs ParamOrder ParamWN Height Temp Humi Pres ProfPairs WNPairs

STR DBL STR INT INT INT STR INT STRARR DBLARR DBLARR DBLARR DBLARR DBLARR DBLARR DBLARR

scalar scalar scalar scalar scalar scalar scalar scalar (NP) (NP) (z) (z) (z) (z) (2,z, NoP) (2,NoP)

- [1] - - - - - - - [cm-1] [km] [K] [g/kg] [hPa] [dB] [cm-1]

Kind of transmission Laser FWHM Atmospheric file name Number of heights Number of parameters (obsolete) Number of no transmission parame-ters (obsolete) Atmospheric file type name Number of wind derivatives Order to identify transmission chan-nels Wavenumber associated to each channel Altitude grid Temperature at each altitude Specific humidity at each altitude Pressure at each altitude Profile transmission data for each channel Wavenumbers associated to each pair

1.1.2 Technical Remarks/Practical Notes If you want to modify this routine or the structure associated with it, traT1data and traT2data variables, you need to modify the structure definition as well (in /src/base/dataStruct.pro).



Page 9 of 79

1.2 PRO IO_AtmosLossGainProfiles The routine is named io_ALGP.pro, the ALPS routine for writing out results calculated by the atmospheric loss and gain modeling routines. Results are written out to the folder speci-fied in the run control file. 1.2.1 Interface Description Name Type Dim I/O Unit Explanation rcfData STRUCT I Run control file structure NoOfPairs INT scalar I - Number of channel pairs to be in-

vestigated Pairs STRARR (2,NoP) I - Name of the channel pairs nwindPairs INT scalar I - Number of wind pairs windChans STRARR (WC) I - Names of wind channels DefocusMode INT scalar I - Mode used for def. loss modeling

(‘p,T,q Atm’ or ‘Simple global static’)

RayleighMode INT scalar I - Mode used for Rayleigh scat. mod-eling (‘p,T,q Atm’ or ‘Simple ana-lytical’)

CompRaylSSRG INT scalar I [km] Switch regulating if solar radiation gain is computed or not

AeroModel INT scalar I - Mode used for aerosol loss model-ing

AerosolLoad INT scalar I - Aerosol load CompClExtLoss INT scalar I - Clouds extinction loss computation

switch SNRMode INT scalar I - Mode defining SNR usage (‘set at

TOA’ or ‘from OSSM’) TScintMode INT scalar I - Mode used for Turb/Scint modeling WindModel INT scalar I - Wind model used CompCompProf INT scalar I - Compute composite profiles switch CompALGPData INT scalar I - Compute ALGP switch CompREPData INT scalar I - Compute REP switch CompWindRetErrs INT scalar I - Compute wind retrieval error switch TxHeight DBL scalar I [km] Orbit height of transmitter satellite RxHeight DBL scalar [km] Orbit height of receiver satellite rawSamplingRate DBL scalar I [Hz] Raw sampling rate rawSamplingSNR _TOA

DBL scalar I [dB] Raw-sampling SNR at TOA

alpha DBL scalar I [1] Ångstrøm exponent rcfFile STR - I - Run control file name ALPSversion STR - I - ALPS version ALPS_TaskId STR - I - ALPS task indentification CreationDate STR - I - Creation date DirRFMInData STR - I - Folder with RFM files TargSpecTrTab STR - I - File name of the RFM Target Spe-

cies transmission profiles TotalTrTab STR - I - File name of the RFM total trans-

mission profile



Page 10 of 79

CompSpecies STR - I - Species name of that composite profile is desired

DirALGPData STR - I - Folder for ALGP data output traT1data STRUCT I Transmission profiles structure NoOfHeights INT scalar I - Number of heights NoOfParams INT scalar I - Number of parameters (obsolete) NoOfNoTranParam INT scalar I - Number of no transmission parame-

ters (obsolete) ParamOrder STRARR (NP) I - Order to identify transmission chan-

nels NWindDerivs INT scalar I - Number of wind derivatives ParamWN DBLARR (NP) I [cm-1] Wavenumber associated to each

channel Height DBLARR (z) I [km] Altitude grid Pres DBLARR (z) I [hPa] Pressure at each altitude Temp Humi

DBLARR DBLARR

(z) (z)

I I

[K] [g/kg]

Temperature at each altitude Specific humidity at each altitude

AtmFile STR - I - Atmospheric file name FwhmLaser DBL scalar I [1] Laser FWHM ALGPdata STRUCT O Structure for ALGP data Gain_toReq Resolution

DBLARR (z) O [dB] Gain from down-sampling from raw sampling rate to required resolution

SNR_rawSampling DBLARR (z) O [dB] Raw-sampling SNR (at TOA) prof. Loss_defocusing DBLARR (z) O [dB] Defocusing loss LossRayleighPairs DBLARR (2,z,NoP) O [dB] Rayleigh scattering loss LossAerosolPairs DBLARR (2,z,NoP) O [dB] Aerosol extinction loss LossTScintPairs DBLARR (2,z,NoP) O [dB] Turb/Scint loss LossBgrAbsorption Pairs

DBLARR (2,z,NoP) O [dB] Background absorption loss

TotalBgrLossPairs DBLARR (2,z,NoP) O [dB] Total background loss TargetSpeciesLoss AbsChannels

DBLARR (z,NoP) O [dB] Target species absorption loss for absorption channels

AvailableSNRPairs DBLARR (2,z,NoP) O [dB] Available SNR (=raw SNR at TOA minus all atm. losses, at raw sam-pling rate)

1.2.2 Technical Remarks/Practical Notes If you want to modify this routine or the structure associated with it, ALGPdata, you need to modify the structure definition as well (in /src/base/dataStruct.pro).



Page 11 of 79

1.3 PRO IO_ObsSystemandSNRProfiles The routine is named io_OSSP.pro, the ALPS routine for writing out results of calcula-tions on link budget profiles between satellites and the SNR profiles. Results are written out to the folder specified in the run control file. 1.3.1 Interface Description Name Type Dim I/O Unit Explanation rcfData STRUCT I Run control file structure DirRFMinData STR scalar I - Folder with RFM files TargSpecTrTab STR scalar I - File name of the RFM Target Spe-

cies transmission profiles TotalTrTab NoOfPairs TxHeight RxHeight TxLaserPower TxOpticsLoss TxAntennaDia meter TxPointingLoss RxOpticsLoss RxAntennaDia meter TxLaserFluctuation DirOSSPData ALPS_TaskId windChans CompALGPData CompREPData CompOSSPData CompOSEPData CompCompProf CompWindRetErrs rcfFile ALPSversion CreationDate

STR INT DBL DBL DBL DBL DBL DBL DBL DBL DBL STR STR STRARR STR STR STR STR STR STR STR STR STR

scalar scalar scalar scalar scalar scalar scalar scalar scalar scalar scalar scalar scalar (WC) scalar scalar scalar scalar scalar scalar scalar scalar scalar

I I I I I I I I I I I I I I I I I I I I I I I

- - [km] [km] [dBW] [dB] [mm] [dB] [dB] [mm] [dB] - - - - - - - - - - - -

File name of the RFM total trans-mission profiles Number of channel pairs to be in-vestigated Orbit height of transmitter satellite Orbit height of receiver satellite Transmitter laser power Transmitter optics loss Transmitter antenna diameter Transmitter pointing loss Receiver optics loss Receiver antenna diameter Transmitter laser fluctuation Folder for OSSP data output ALPS task indentification Names of wind channels Compute ALGP switch Compute REP switch Compute OSSP switch Compute OSEP switch Compute composite profiles switch Compute wind retrieval error switch Run control file name ALPS version Creation date

traT1data STRUCT I Transmission profiles structure KindofTran FwhmLaser AtmFile NoOfHeights NoOfParams NoOfNoTranParam AtmRegion NWindDerivs ParamOrder

STR DBL STR INT INT INT STR INT STRARR

scalar scalar scalar scalar scalar scalar scalar scalar (NP)

I I I I I I I I I

- [1] - - - - - - -

Kind of transmission Laser FWHM Atmospheric file name Number of heights Number of parameters (obsolete) Number of no transmission parame-ters (obsolete) Atmospheric file type name Number of wind derivatives Order to identify transmission chan-



Page 12 of 79

ParamWN Height Temp Humi Pres ProfPairs WNPairs

DBLARR DBLARR DBLARR DBLARR DBLARR DBLARR DBLARR

(NP) (z) (z) (z) (z) (2,z,NoP) (2,NoP)

I I I I I I I

[cm-1]

[km] [K] [g/kg] [hPa] [dB] [cm-1]

nels Wavenumber associated to each channel Altitude grid Temperature at each altitude Specific humidity at each altitude Pressure at each altitude Profile transmission data for each channel Wavenumber associated to each pair

OSSPdata STRUCT O Structure for OSSP data LinkBudget AvailableSNR

DBLARR DBLARR

(2,z,NoP) (2,z,NoP)

O O

[dBW] [dB]

Link budget received power profiles Available SNR profiles (=raw SNR minus all atm. losses, at raw sam-pling rate from OSSM)

1.3.2 Technical Remarks/Practical Notes If you want to modify this routine or the structure associated with it, OSSPdata, you need to modify the structure definition as well (in /src/base/dataStruct.pro).



Page 13 of 79

1.4 PRO IO_ObsSystemErrorProfiles The routine is named io_OSEP.pro, the ALPS routine for writing out results of noise cal-culations. Results are written out to the folder specified in the run control file. 1.4.1 Interface Description Name Type Dim I/O Unit Explanation rcfData STRUCT I Run control file structure DirRFMinData STR scalar I - Folder with RFM files TargSpecTrTab STR scalar I - File name of the RFM Target Spe-

cies transmission profiles TotalTrTab NoOfPairs TxHeight RxHeight TxLaserPower TxOpticsLoss TxAntennaDia meter TxPointingLoss RxOpticsLoss RxAntennaDia meter TxLaserFluctuation DirOSSPData ALPS_TaskId windChans CompALGPData CompREPData CompOSSPData CompOSEPData CompCompProf CompWindRetErrs rcfFile ALPSversion CreationDate

STR INT DBL DBL DBL DBL DBL DBL DBL DBL DBL STR STR STRARR STR STR STR STR STR STR STR STR STR

scalar scalar scalar scalar scalar scalar scalar scalar scalar scalar scalar scalar scalar (WC) scalar scalar scalar scalar scalar scalar scalar scalar scalar

I I I I I I I I I I I I I I I I I I I I I I I

- - [km] [km] [dBW] [dB] [mm] [dB] [dB] [mm] [dB] - - - - - - - - - - - -

File name of the RFM total trans-mission profiles Number of channel pairs to be in-vestigated Orbit height of transmitter satellite Orbit height of receiver satellite Transmitter laser power Transmitter optics loss Transmitter antenna diameter Transmitter pointing loss Receiver optics loss Receiver antenna diameter Transmitter laser fluctuation Folder for OSSP data output ALPS task indentification Names of wind channels Compute ALGP switch Compute REP switch Compute OSSP switch Compute OSEP switch Compute composite profiles switch Compute wind retrieval error switch Run control file name ALPS version Creation date

traT1data STRUCT I Transmission profiles structure KindofTran FwhmLaser AtmFile NoOfHeights NoOfParams NoOfNoTranParam AtmRegion NWindDerivs ParamOrder

STR DBL STR INT INT INT STR INT STRARR

scalar scalar scalar scalar scalar scalar scalar scalar (NP)

I I I I I I I I I

- [1] - - - - - - -

Kind of transmission Laser FWHM Atmospheric file name Number of heights Number of parameters (obsolete) Number of no transmission parame-ters (obsolete) Atmospheric file type name Number of wind derivatives Order to identify transmission chan-nels



Page 14 of 79

ParamWN Height Temp Humi Pres ProfPairs WNPairs

DBLARR DBLARR DBLARR DBLARR DBLARR DBLARR DBLARR

(NP) (z) (z) (z) (z) (2,z,NoP) (2,NoP)

I I I I I I I

[cm-1] [km] [K] [g/kg] [hPa] [dB] [cm-1]

Wavenumber associated to each channel Altitude grid Temperature at each altitude Specific humidity at each altitude Pressure at each altitude Profile transmission data for each channel Wavenumber associated to each pair

OSEPdata STRUCT O Structure for OSEP data Tx_Noise Rx_Noise Sc_Noise To_Noise

DBLARR DBLARR DBLARR DBLARR

(2,z,NoP) (2,z,NoP) (2,z,NoP) (2,z,NoP)

O O O O

[dBW] [dBW] [dBW] [dBW]

Transmitter induced noise Receiver induced noise Scintillation induced noise Total noise

1.4.2 Technical Remarks/Practical Notes If you want to modify this routine or the structure associated with it, OSEPdata, you need to modify the structure definition as well (in /src/base/dataStruct.pro).



Page 15 of 79

1.5 PRO IO_RetrievalErrorProfiles The routine is named io_REP.pro, the ALPS routine for writing out results calculated by the retrieval error profiles modeling routines. Results are written out to the folder specified in the run control file. 1.5.1 Interface Description Name Type Dim I/O Unit Explanation rcfData STRUCT I Run control file structure NoOfPairs INT scalar I - Number of channel pairs to be in-

vestigated Pairs STRARR (2,NoP) I - Name of the channel pairs DefocusMode INT scalar I - Mode used for def. loss modeling

(‘p,T,q Atm’ or ‘Simple global stat-ic’)


CompRaylSSRG INT scalar I [km] Switch regulating if solar radiation gain is computed or not

AeroModel INT scalar I - Mode used for aerosol loss model-ing

AerosolLoad INT scalar I - Aerosol load CompClExtLoss INT scalar I - Clouds extinction loss computation


TOA’ or ‘from OSSM’) TScintMode INT scalar I - Mode used for Turb/Scint modeling WindModel INT scalar I - Wind model used CompCompProf INT scalar I - Compute composite profiles switch CompALGPData INT scalar I - Compute ALGP switch CompREPData INT scalar I - Compute REP switch CompWindRetErrs INT scalar I - Compute wind retrieval error switch rcfFile STR - I - Run control file name ALPSversion STR - I - ALPS version ALPS_TaskId STR - I - ALPS task indentification CreationDate STR - I - Creation date DirRFMInData STR - I - Folder with RFM files TargSpecTrTab STR - I - File name of the RFM Target Spe-


mission profile TxHeight DBL scalar I [km] Orbit height of transmitter satellite RxHeight DBL scalar [km] Orbit height of receiver satellite rawSamplingRate DBL scalar I [Hz] Raw sampling rate SNR_rawSampling Rate


alpha DBL scalar I [1] Ångstrøm exponent CompSpecies STR - I - Species name of that composite

profile is desired



Page 16 of 79

windChans STRARR (WC) I - Names of wind channels DirREPData STR - I - Folder for REP data output traT1data STRUCT I Transmission profiles structure NoOfHeights INT scalar I - Number of heights Height DBLARR (z) I [km] Altitude grid Pres DBLARR (z) I [hPa] Pressure at each altitude Temp DBLARR (z) I [K] Temperature at each altitude Humi DBLARR (z) I [g/kg] Humidity at each altitude AtmFile STR - I - Atmospheric file name FwhmLaser DBL scalar I [1] Laser FWHM ALGPdata STRUCT I Structure for ALGP data AvailableSNRPairs DBLARR (2,z,NoP) I [dB] Available SNR (=raw SNR at TOA

minus all atm. losses, at raw sam-pling rate)

OSSPdata STRUCT I Structure for OSSP data AvailableSNR DBLARR (2,z,NoP) I [dB] Available SNR profiles (=raw SNR

minus all atm. losses, at raw sam-pling rate from OSSM)

REPbasedata STRUCT O Retrieval error profiles structure SNRatReqResol Pairs

DBLARR (2,z,NoP) O [dB] SNR at required vertical resolution for channel pairs (with the Available SNR either from ALGP or OSSP, dependent on “SNR Mode”)

TranErrorPairs DBLARR (2,z,NoP) O [%] SNR-based transmission errors for channel pairs

DiffLogTranErrors DBLARR (z,NoP) O [%] Differential log-transmission error DiffLogTranRela-tiveErrors

DBLARR (z,NoP) O [%] Differential log-transmission rela-tive error

SpeciesAbsCoeffEr-rors

DBLARR (z,NoP) O [%] Species absorption coefficient error

SpeciesProfileErrors DBLARR (z,NoP) O [%] Species profile retrieval error MonthlyMeanPro-fileErrors

DBLARR (z,NoP) O [%] Monthly-mean profile retrieval error

REPH2Odata STRUCT O Composite water profiles structure Avail-ableSNR_abs_comp

DBLARR (z) O [dB] SNR for composite absorption channel

Avail-ableSNR_ref_comp

DBLARR (z) O [dB] SNR for composite reference chan-nel

Tran Error_abs_comp

DBLARR (z) O [%] SNR-based transmission error for composite absorption channel

TranError_ref_comp DBLARR (z) O [%] SNR-based transmission error for composite reference channel

DiffLog-TranErr_comp

DBLARR (z) O [%] Differential log-transmission error for composite

DiffLogTranRela-tiveErr_comp

DBLARR (z) O [%] Differential log-transmission rela-tive error for composite

SpeciesAbsCoef-fErr_comp

DBLARR (z) O [%] Species absorption coefficient error for composite

SpeciesPro-fileErr_comp

DBLARR (z) O [%] Species profile retrieval error for composite

MonthlyMeanPro-fileErr_comp

DBLARR (z) O [%] Monthly-mean profile retrieval error for composite

REPwindErrdata STRUCT O



Page 17 of 79

V_los DBLARR (z) O [m/s] Line-of-sight wind velocity profile DDiffTrandB_w1 w2

DBLARR (z) O [dB] Transmission differences of wind channels

FreqErr_fsraw DBL scalar O [1] Raw frequency error df/f at 50 Hz sampling

BasicFreqErr DBLARR (z) O [1] Frequency error df/f at required resolution

DDiffLogTranErr_ w1w2

DBLARR (z) O [%] Double-diff (w1-w2) log-transmission error

DiffLogTranErr_w1 w2_0_Mod

DBLARR (z) O [%] Zero-wind differential log-transmission model error

TotalDDiffLogTran RelErr

DBLARR (z) O [%] Total double differential log-transmission relative error

TotaldTrdNuRelErr _Mod

DBLARR (z) O [%] Total differential log-transmission derivative model relative Error

V_los_StatistRelErr DBLARR (z) O [%] Line-of-sight wind statistical rela-tive error

V_los_StatistErr DBLARR (z) O [m/s] Statistical wind retrieval error V_los_SystematErr DBLARR (z) O [m/s] Single-profile systematic wind error V_los_ProfileErr DBLARR (z) O [m/s] l.o.s.wind profile retrieval error 1.5.2 Technical Remarks/Practical Notes If you want to modify this routine or the structures associated with it (REPbasedata, REPH2Odata, REPwindErrdata) you need to modify the related structure definitions as well (in /src/base/dataStruct.pro).



Page 18 of 79

(intentionally left blank/back-page if double-sided print)



Page 19 of 79

2 Atmospheric Loss/Gain Modeling Routines The Atmospheric Loss and Gain Modeling Routines can be found in the directory /src/base/ALGM. The routine alpsALGM.pro is the envelope routine (section 2.1). It provides the atmospheric losses/gains of reference and absorption channels including defocus-ing loss, Rayleigh scattering loss, gain from Rayleigh scattered solar radiation, aerosol and cloud extinction loss. Every loss/gain is calculated in a separate routine (sections 2.2 to 2.6). Furthermore alpsALGM computes the resolution gain from down-sampling the SNR at raw sampling rate to the required vertical resolution as well as the available SNR (at raw sampling rate) after atmospheric losses are subtracted from the raw SNR specified at TOA. These pa-rameters are computed directly in the alpsALGM envelope routine (see section 2.1 below). The defocusingLoss.pro routine (section 2.2) contains algorithms to obtain the defo-cusing loss, which takes into account that, although a laser beam is used, the propagating rays are not perfectly parallel but diverge, leading to a loss of light intensity in the line of sight. The rayleighScatteringLoss.pro routine (section 2.3) calculates the radiation loss mainly for the short-wave infrared wavelengths due to Rayleigh scattering. The rayleigh-ScatSolarRadGain.pro routine (section 2.4) calculates the received intensity gain through Rayleigh-scattered solar radiation which is scattered into the receiver telescope. The aerosolExtinctionLoss.pro routine (section 2.5) carries out the calculations of the extinction loss through aerosols based on empirical modeling. The cloudsExtinc-tionLoss.pro routine (section 2.6) takes into account the intensity loss through water and ice cloud extinction for short-wave infrared wavelengths. 2.1 PRO AtmosLossGainModeling (envelope routine) The routine alpsALGM.pro controls the calculations regarding the Atmospheric Loss and Gain Modeling. It computes the resolution gain, atmospheric losses/gains of reference and absorption channels, and available SNR, as noted in the introduction above. Each of these three components is addressed in the algorithm description below. 2.1.1 Interface Description Name Type Dim I/O Unit Explanation rcfData STRUCT I Run control file structure NoOfPairs INT scalar I - Number of channel pairs to be in-

vestigated Pairs STRARR (2,NoP) I - Name of the channel pairs nwindPairs INT scalar I - Number of wind pairs windChans STRARR (WC) I - Names of wind channels DefocusMode INT scalar I - Mode used for def. loss modeling

(‘p,T,q Atm’ or ‘Simple global stat-ic’)


CompRaylSSRG INT scalar I [km] Switch regulating if solar radiation



Page 20 of 79

gain is computed or not AeroModel INT scalar I - Mode used for aerosol loss model-

ing AerosolLoad INT scalar I - Aerosol load CompClExtLoss INT scalar I - Clouds extinction loss computation


TOA’ or ‘from OSSM’) TScintMode INT scalar I - Mode used for Turb/Scint modeling WindModel INT scalar I - Wind model used CompCompProf INT scalar I - Compute composite profiles switch CompALGPData INT scalar I - Compute ALGP switch CompREPData INT scalar I - Compute REP switch CompWindRetErrs INT scalar I - Compute wind retrieval error switch TxHeight DBL scalar I [km] Orbit height of transmitter satellite RxHeight DBL scalar [km] Orbit height of receiver satellite rawSamplingRate DBL scalar I [Hz] Raw sampling rate rawSamplingSNR _TOA


alpha DBL scalar I [1] Ångstrøm exponent rcfFile STR - I - Run control file name ALPSversion STR - I - ALPS version ALPS_TaskId STR - I - ALPS task indentification CreationDate STR - I - Creation date DirRFMInData STR - I - Folder with RFM files TargSpecTrTab STR - I - File name of the RFM Target Spe-


mission profile CompSpecies STR - I - Species name of that composite

profile is desired DirALGPData STR - I - Folder for ALGP data output traT1data STRUCT I Species Transmission profiles struc-

ture KindofTran FwhmLaser AtmFile NoOfHeights NoOfParams NoOfNoTranParam AtmRegion NWindDerivs ParamOrder ParamWN Height Temp Pres ProfPairs WNPairs

STR DBL STR INT INT INT STR INT STRARR DBLARR DBLARR DBLARR DBLARR DBLARR DBLARR

scalar scalar scalar scalar scalar scalar scalar scalar (NP) (NP) (z) (z) (z) (2,z, NoP) (2,NoP)

I I I I I I I I I I I I I I I

[cm-1] [km] [K] [hPa] [dB] [cm-1]

Kind of transmission Laser FWHM Atmospheric file name Number of heights Number of parameters (obsolete) Number of no transmission parame-ters (obsolete) Atmospheric file type name Number of wind derivatives Order to identify transmission chan-nels Wavenumber associated to each channel Altitude grid Temperature at each altitude Pressure at each altitude Profile transmission data for each channel Wavenumber associated to each pair



Page 21 of 79

traT2data STRUCT I Total Transmission profiles struc-

ture KindofTran FwhmLaser AtmFile NoOfHeights NoOfParams NoOfNoTranParam AtmRegion NWindDerivs ParamOrder ParamWN Height Temp Pres ProfPairs WNPairs

STR DBL STR INT INT INT STR INT STRARR DBLARR DBLARR DBLARR DBLARR DBLARR DBLARR

scalar scalar scalar scalar scalar scalar scalar scalar (NP) (NP) (z) (z) (z) (2,z, NoP) (2,NoP)

I I I I I I I I I I I I I I I

[cm-1] [km] [K] [hPa] [dB] [cm-1]

Kind of transmission Laser FWHM Atmospheric file name Number of heights Number of parameters (obsolete) Number of no transmission pa Wavenumber associated to each pair parameters (obsolete) Atmospheric file type name Number of wind derivatives Order to identify transm. channels Wavenumber associated to each pair channel Altitude grid Temperature at each altitude Pressure at each altitude Profile transmission data for each channel

ALGPdata STRUCT O Structure for ALGP data Gain_toReq Resolution

DBLARR (z) O [dB] Gain from down-sampling from raw sampling rate to required resolution

SNR_rawSampling DBLARR (z) O [dB] Raw-sampling SNR (at TOA) prof. Loss_defocusing DBLARR (z) O [dB] Defocusing loss LossRayleighPairs DBLARR (2,z,NoP) O [dB] Rayleigh scattering loss LossAerosolPairs DBLARR (2,z,NoP) O [dB] Aerosol extinction loss LossTScintPairs DBLARR (2,z,NoP) O [dB] Turb/Scint loss LossBgrAbsorption Pairs

DBLARR (2,z,NoP) O [dB] Background absorption loss

TotalBgrLossPairs DBLARR (2,z,NoP) O [dB] Total background loss TargetSpeciesLoss AbsChannels

DBLARR (z,NoP) O [dB] Target species absorption loss for absorption channels

AvailableSNRPairs DBLARR (2,z,NoP) O [dB] Available SNR (=raw SNR at TOA minus all atm. losses, at raw sam-pling rate)

2.1.2 Algorithmic Description Computation of resolution gain:

Starting point for the computation of the resolution gain GResol is the raw-sampling SNR at TOA (from the rcfData or otherwise internal default value of 27 dB), SNRf_s,raw, at the raw sampling rate fs,raw (also from the rcfData, typically 50 Hz). GResol is the quantity that converts SNRf_s,raw to an SNR consistent with the required vertical resolution (of 1-2 km). For this pur-pose, the downsampling gain, Gds, is first computed,

filts,

raws, ds log10[dB] f

fG ⋅= , Eq. 1



Page 22 of 79

which results from downsampling of fs,raw to a filtered sampling rate, fs,filt, where we adopt fs,filt = 2 Hz as baseline, equivalent to a unit 1 Hz observational bandwidth according to Nyquist’s sampling theorem. Secondly, the resolution-adjustment gain, Gresadj, is computed,

filt

target resadj log10[dB] dz

dzG ⋅= , with Eq. 2

filts,

scanfilt 5.0 f

Vdz⋅

= ,

Vscan [km/s] = {0.3, 2.8, 3, 3.15, 3.2, 3.2} at z [km] = {0, 25, 30, 35, 40, 120} (linear interpolation between z levels),

which scales the vertical resolution matching 1 Hz bandwidth, dzfilt, to the required vertical resolution, dztarget, where dzfilt is obtained based on the LEO-LEO vertical scan velocity, Vscan, empirically modeled to represent the typical set/rise velocity of occultation rays during LEO-LEO occultation events. Note that if dzfilt is greater than dztarget (1-2 km), occurring at heights where Vscan > 2 km/s, Gresadj becomes negative, i.e., a loss.

The resolution gain at required vertical resolution dztarget is then obtained from adding down-sampling and resolution-adjustment gain,

resadjds Resol ]dB[ GGG += . Eq. 3

GResol is later used by the retrieval error modeling (section 6) to convert the available SNR at raw sampling rate (used here from ALGM, see below, or from OSSM, see section 4, depend-ing on “SNR Mode”) to the SNR at required resolution.

Computation of atmospheric losses/gains:

Performed by the routines described in sections 2.2 to 2.6, called by this envelope routine.

Computation of available SNR at raw sampling rate from raw-sampling SNR at TOA:

Based on SNRf_s,raw used as profile over all height levels, the available SNR for the absorption and reference channels, SNRAbs and SNRRef, is computed,

TSpBgrrawf_s, Abs ]dB[ LLSNRSNR −−= , TSpBgrrawf_s, Ref ]dB[ +−= LSNRSNR ,

Eq. 4

where LBgr, LTSp, and LBgr+TSp (all in units [dB]) are the total background loss, target species absorption loss, and background plus (small residual) target species absorption loss in refer-ence channels, respectively. SNRAbs and SNRRef are obtained at the given raw sampling rate. Thereby the total background loss LBgr is modeled as the sum of defocusing loss, LDef, Rayleigh scattering loss, LR, aerosol extinction loss, LA, turbulence/scintillation loss, LTS, and background absorption loss coming from residual absorption by other gases than the target species in consideration, LBgrAbs:

BgrAbsTSARDefBgr ]dB[ LLLLLL ++++= . Eq. 5



Page 23 of 79

In case of a reference channel, LBgr+TSp is used, which has just added to LBgrAbs in Eq. 5 the target species absorption loss as well, which is for reference channels a small residual absorp-tion similar to all the other gases contributing to LBgrAbs. Note that since LBgr of an absorption channel and LBgr+TSp of its associated reference channel will be closely the same due to the small channel spacing (relative frequency difference within ~0.5%), the total background signal will be eliminated to high accuracy by log-transmission differencing between the channels, leaving besides the target species signal only a very small differencing residual error to be co-modeled in LIO retrieval processing (differ-encing residual error used in the retrieval error modeling, section 6). The target species absorption loss LTSp and the background absorption loss LBgrAbs are com-puted from the RFM/HITRAN/FASCODEatm modeling system (input via the traT1data and traT2data structures). On the inclusion of component losses within LBgr in the current version (see Part 1, section 2), the turbulence/scintillation loss LTS is still a code feature but meanwhile obsolete and set to zero; scintillations are modeled as observation system error component (see section 5.4). Also the Rayleigh-scattered solar radiation gain and the clouds extinction loss are not included in LBgr due to their special character (the former generally negligible, the latter generally extin-guishing signals fully into noise) but available as separate gain/loss profiles information. In future these may be integrated for completeness as options in the total loss modeling as well.



Page 24 of 79

2.2 PRO DefocusingLoss The program defocusingLoss offers two model modes to compute the defocusing loss: the more elaborated p,T,q Atm Defocusing Loss Model (see 2.2.2.1) and the Simple global static Defocusing Loss Model (see 2.2.2.2). 2.2.1 Interface Description Name Type Dim I/O Unit Explanation rcfData STRUCT I Run control file structure DefocusMode INT scalar I - Mode used for def. loss modeling (‘p,

T, q Atm’ or ‘Simple global static’) TxHeight DBL scalar I [km] Transmitter Height RxHeight DBL scalar I [km] Receiver Height Height=z DBLARR (z) oI [km] Altitude grid Pres=p DBLARR (z) oI [hPa] Pressure Temp=T DBLARR (z) oI [K] Temperature Humi=q DBLARR (z) oI [g/kg] Specific Humidity BA=BendAngle DBLARR (z) oO [mrad] Bending Angle LossDefocus DBLARR (z) O [dB] Defocusing Loss 2.2.2 Algorithmic Description 2.2.2.1 p, T, q Atm Defocusing Loss Model Constants used: Rgas, Mair, g0, RE, Rd, Rw, aw, bw, c1, c2, c3, d1, d2, e1 (see List of Constants) Computation of atmospheric scale height:

)()(

10)(air

gas3scale zgM

zTRzH

⋅⋅

⋅= − , where

2

E

E0)( ⎟⎟

⎠

⎞⎜⎜⎝

⎛+

⋅=zR

Rgzg

Eq. 6

Hscale(z) … scale height [km] T(z) … temperature [K] g(z) … gravitational acceleration [m/s2] z … height [km] Computation of water vapor pressure:

)(

)()()(zqba

zqzpzeww ⋅+⋅= Eq. 7

e(z) water vapor pressure [hPa] p(z) …pressure [hPa] q(z) specific humidity [kg/kg]



Page 25 of 79

Computation of refractivity and refractive index by the modified-Edlén formula: (done in a separate subroutine VIR_Refractivity; in /src/base/virRefrac.pro)

( ) ( ) )( )()()( 11

2

31

1

21

22

zeezTzp

dc

dcczN ⋅−⎟⎟

⎠

⎞⎜⎜⎝

⎛

−+

−+=

λλ

( ) ( )zN+=zn 6101 − Eq. 8

N(z) refractivity [N-units] n(z) refractive index [1] λ wavelength [μm] The coefficients in this modified-Edlen formula are consistent with (and derived from) those of the elaborated optical refractivity formula of Boensch and Potulski (1998). Computation of atmospheric impact parameter and bending angle:

( )zRznza E +⋅= )()( Eq. 9

( )

( ))(

)(1210)(

)()(210)(

where,)()(1)()()(

scale

6

scale

3

zHzazb

zHzaza

zNzbzNzaz

α

α

αα

⋅−⋅=

⋅⋅=

⋅+⋅⋅=

−

− π

α

Eq. 10

a(z) … impact parameter [km] α (z) … bending angle [mrad] aα(z) … 1st order coefficient [mrad/N-units] bα(z) … 2nd order coefficient [1/N-units] Computation of defocusing loss:

( )( ) )(cos)(

)(cos)(

arcsin)(

arcsin)(

where,dd

)()()()(101log10)(

RxERx

TxETx

RxE

E

TxE

E

RxTx

RxTx3def

zzRzDzzRzD

zRzRz

zRzRz

azDzDzDzDzL

Rx

Tx

Rx

Tx

Ψ⋅+=Ψ⋅+=

⎟⎟⎠

⎞⎜⎜⎝

⎛++=Ψ

⎟⎟⎠

⎞⎜⎜⎝

⎛++=Ψ

⎟⎟⎠

⎞⎜⎜⎝

⎛⋅

+⋅⋅−⋅= − α

Eq. 11

Ldef(z) … defocusing loss [dB] ΨTx(z), ΨTx(z) … zenith angle of the ray at the transmitter/receiver position [rad] DTx(z), DRx(z) … distance between ray tangent point and transmitter/receiver [km] zTx, zRx … height of the transmitter/receiver [km]



Page 26 of 79

2.2.2.2 Simple Global Static Defocusing Loss Model This model is an empirical model based on hinge points for Ldef and defocusing loss scale heights Hdef as follows:

Ldef, 0km = 9 dB Ldef, 20km = 1.5 dB Ldef, 25km = 0.7 dB Hdef, troposphere = 11.5 km Hdef, stratosphere = 6.5 km

Using these hinge points, Ldef_z is computed for all heights as follows:

Below 10 km: ⎟⎟⎠

⎞⎜⎜⎝

⎛ −⋅=re troposphedef,

0km def,def_z exp)( HzLzL

10 to 20 km: ( )1010

10exp)( 10km def,20km def,re troposphedef,

0km def,def_z −⋅⎟⎟⎠

⎞⎜⎜⎝

⎛ −+⎟⎟⎠

⎞⎜⎜⎝

⎛ −⋅= zLL

HLzL

20 to 25 km: ( )205

)( 20km def,25km def,20km def,def_z −⋅⎟⎟⎠

⎞⎜⎜⎝

⎛ −+= z

LLLzL

Above 25 km:

( )⎟⎟⎠

⎞⎜⎜⎝

⎛ −−⋅=restratosphe def,

25km def,def_z25exp)(

HzLzL

Eq. 12

)()( def_zdef zLzL = Eq. 13



Page 27 of 79

2.3 PRO RayleighScatteringLoss The program rayleighScatteringLoss offers two model modes to compute the ray-leigh scattering loss: the more elaborated p, T Atm Rayleigh Scattering Model (see 2.3.2.1) and the Simple analytical Rayleigh Scattering Model (see 2.3.2.2). 2.3.1 Interface Description Name Type Dim I/O Unit Explanation rcfData STRUCT I Run control file structure RayleighMode INT scalar I - Mode used for Rayleigh scattering

modeling (‘p, T, q Atm’ or ‘Simple analytical’)

lambda DOUBLE scalar I [nm] Wavelength Height=z DBLARR (z) oI [km] Altitude grid Pres=p DBLARR (z) oI [hPa] Pressure Temp=T DBLARR (z) oI [K] Temperature Humi=q DBLARR (z) oI [g/kg] Specific Humidity sigmaR DBLARR (z) O [km-1] Rayleigh scattering coefficient OptThickR DBLARR (z) O [1] Rayleigh optical thickness LossRayl DBLARR (z) O [dB] Rayleigh scattering loss 2.3.2 Algorithmic Description 2.3.2.1 p, T, q Atm Rayleigh Scattering Model Constants used: kB (see List of Constants) Computation of refractivity and refractive index: see Eq. 8 (modified-Edlen formula) in sec-tion 2.2.2.1. Computation of air density:

)()(10)(

B

2

air zTkzp=zn

⋅⋅ Eq. 14

nair(z) … air density [m-3] p(z) … pressure [hPa] T(z) … temperature [K] Computation of Rayleigh scattering coefficient:

( )4air

23

R 31)(321000),(

λπλσ

⋅⋅−⋅⋅=

nznz Eq. 15

σR(z,ν) … rayleigh scattering coefficient [km-1] λ … wavelength [m]



Page 28 of 79

Computation of Rayleigh scattering loss:

( )( )

effRR

RR

),(),( where,),(explog10),(

lzzzzL

⋅=−⋅−=

λσλτλτλ

Eq. 16

LR(z, λ) … rayleigh scattering loss [dB] τR(z, λ) … rayleigh optical thickness [1] leff … effective path length [km]; set to 300 km 2.3.2.2 Simple Analytical Rayleigh Scattering Model Constants used: n0 (see List of Constants) Computation of simple global-mean air density:

⎟⎠⎞

⎜⎝⎛ −⋅=

Hznzn exp)( 0air Eq. 17

nair(z) … air density [m-3] z … height [km] H … scale height [km]; set to 7 km Computation of simple global-mean refractive index:

)(1)( airn znfzn ⋅+= Eq. 18

Computation of Rayleigh scattering coefficient and Rayleigh scattering loss: see Eq. 15 and Eq. 16; same formulations used here.



Page 29 of 79

2.4 PRO RayleighScatteredSolarRadGain The program rayleighScatSolarRadGain offers computation of solar radiation scat-tered into the receiver telescope by Rayleigh scattering, together with some intermediate quantities such as Rayleigh-scattered solar radiation towards the receiver (see section 2.4.1). 2.4.1 Interface Description Name Type Dim I/O Unit Explanation rcfData STRUCT I Run control file structure RayleighMode CompRaylSSRG

INT INT

Scalar scalar

I I

- Mode used for Rayleigh scatter-ing modeling (‘p, T, q Atm’ or ‘Simple analytical’) Switch regulating if solar radia-tion gain is computed or not

lambda DOUBLE scalar I [nm] Wavelength Height=z DBLARR (z) oI [km] Altitude grid Pres=p DBLARR (z) oI [hPa] Pressure Temp=T DBLARR (z) oI [K] Temperature Humi=q DBLARR (z) oI [g/kg] Specific Humidity SolIrradianceTOA DOUBLE scalar O [Wm-2nm-1] Top-of-Atmosphere incoming

solar irradiance RaylScatSol-RadGaintoRx

DBLARR (z) O [Wm-2nm-1sr-1] Rayleigh-scattered solar radia-tion towards Rx

RaylScatSolRadGain DBLARR (z) O [W] Rayleigh-scattered solar radia-tion gain at Rx

2.4.2 Algorithmic Description Constants used: cl1, cl2, σ, Tsun, Ssun,1AU (see List of Constants) Computation of air density and refractive index: After Eq. 14 and Eq. 8 when using the p, T, q Atm Rayleigh Scattering Model; after Eq. 17 and Eq. 18 when using the Simple Analytical Rayleigh Scattering Model Computation of directional Rayleigh scattering coefficient:

( )

⎟⎟

⎠

⎞

⎜⎜

⎝

⎛⎟⎟⎠

⎞⎜⎜⎝

⎛⎟⎠⎞

⎜⎝⎛ ⋅⋅⎟

⎠⎞

⎜⎝⎛ ⋅+⋅=

⋅⋅⋅

−⋅⋅=

2

SS

R4air

22

180cos

180sin175.0

where,)(31)(81000),(

ππ

λπλγ

azp

pzn

znz

R

R

Eq. 19

γR(z,λ) … directional Rayleigh scattering coefficient [km-1sr-1] n(z), nair(z) … refractive index [1], air density [m-3] λ … wavelength [m] pR …Rayleigh scattering normalized phase function (the angle in parentheses is the scattering angle formulated as function of solar zenith and azimuth angles) zS … solar zenith angle at tangent point (TP) [deg]; baseline setting: 60° aS … solar azimuth angle at TP (relative to occultation plane) [deg]; baseline setting: 0°



Page 30 of 79

Computation of incoming solar irradiance at top-of-atmosphere:

4sunsun

sun

l25l1

sun

sunsun

sun,1AUTOAsun,

1exp

1)(

ere wh,)(

TE

Tc

cB

BE

SI

⋅=

−⎟⎟⎠

⎞⎜⎜⎝

⎛⋅

⋅=

⋅⋅=

σ

λλ

λ

πλ

Eq. 20

Isun,TOA(λ) … incoming solar irradiance at top-of-atmosphere [Wm-2nm-1] λ … wavelength [nm] Bsun(λ) … sun’s specific radiation at wavelength λ (black body radiation) [Wm-2nm-1sr-1] Esun … total radiation of sun (Stefan-Boltzmann law) [Wm-2] Computation of available solar intensity in the atmosphere:

( )),(exp)(),( RTOAsun,sun λτλλ zIzI −⋅= Eq. 21Isun(z,λ) … available solar intensity [Wm-2nm-1] τR(z,λ) … Rayleigh optical thickness [1]; set to 01 Computation of Rayleigh-scattered solar radiation towards the receiver:

effsunRtoRxR, ),(),(),( lzIzzR ⋅⋅= λλγλ Eq. 22

RR,toRx(z,λ) … Rayleigh-scattered solar radiation towards the receiver [Wm-2nm-1sr-1] leff … effective path length [km]; set to 300 km Computation of Rayleigh scattered solar radiation gain at the receiver:

),(104

),( toRxR,2

Rx6

RxR λαπλ zRBWAzG ⋅⋅⋅= − Eq. 23

GR(z,λ) … Rayleigh-scattered solar radiation gain at the receiver [W] ARx … receiver telescope reception area [m2]; baseline setting: 0.1 m2 (~36 cm circular

telescope) α Rx … receiver telescope aperture full angle [mrad]; baseline setting: 1.0 mrad (~3 km vertical width at tangent point, which is ~3000 km apart from the Rx telescope) BW … receiver channels observation bandwidth [nm]; baseline setting: 0.15 nm (typical spectral/filter resolution spec for LIO receiver design)

1 for >1.5µm / >2µm even grazing-incidence solar transmission is >95% / >99% down to z < 2 km, i.e., neglect-ing Rayleigh scattering losses to the incoming irradiance is basically a very good approximation. Considering also the simultaneous absorption processes that attenuate the solar intensity along its atmospheric paths this approximation is a good upper limit, i.e., solar radiation gain will always be lower than the estimate here in case of significant absorption. Regarding ACCURATE, this will apply to the absorption channels where the present estimates are upper bounds. In the treatment of actual data any solar radiation gain detected above detector noise level (baseline spec ~5⋅10-13 W), by the before/after-pulse co-measurement of background radiation, would be subtracted from the raw-received data.



Page 31 of 79

2.5 PRO AerosolExtinctionLoss The program aerosolExtinctionLoss offers two model modes to compute the aerosol extinction: the more elaborated SAGE-II based Aerosol extinction Model (see 2.5.2.1) and the more simple Lowtran based Aerosol extinction Model (see 2.5.2.2). 2.5.1 Interface Description Name Type Dim I/O Unit Explanation rcfData STRUCT I Run control file structure AeroModel INT scalar I - Mode used for aerosol loss modeling

(‘SAGE II based’ or ‘LOWTRAN based’)

AerosolLoad INT scalar I - Aerosol load (‘background’ or ‘me-dium’ or ‘volcanic’; ‘medium’ for mode ‘SAGE II based’ only)

alpha INT scalar I [1] Ångstrøm exponent (for ‘LOWTRAN based’ only)

lambda DOUBLE scalar I [nm] Wavelength z DBLARR (z) I [km] Height AtmRegion STRING - I - Name of latitude band kappaAero DBLARR (z) O [km-1] Aerosol extinction coefficient OptThickA DBLARR (z) O [1] Aerosol optical thickness LossAero DBLARR (z) O [dB] Aerosol extinction loss 2.5.2 Algorithmic Description 2.5.2.1 SAGE-II based Aerosol extinction Model No constants of List of Constants used. This model is based on a parameterization for the aerosol extinction coefficient [km-1] (valid for the reference wavelength λ0, which is 1020 nm for this model) derived from SAGE-II aerosol extinction measurements. The parameterization is latitude (3 latitude bands: tropical, mid-latitude, high latitudes) and height dependent (10 height steps between 0 km and 120 km) and distinguishes between background, medium and volcanic aerosol load. It is consistent, as a simplified version, with the aerosol extinction model implemented in the EGOPS software (EGOPS, 2009). Which latitude band and aerosol load is used is driven by the run control file. Furthermore, a height-dependent parameterization for the Ångstrøm exponent is given, which is also derived from SAGE-II measurements. κλ0(z) [km-1], the aerosol extinction coefficient profile at λ0 corresponding to the input height vector z [km], is computed via log-linear interpolation of the parameterized coefficient pro-file. Equally αA(z) [1], the Ångstrøm exponent profile corresponding to the input height vec-tor z [km], is computed vial log-linear interpolation of the parameterized Ångstrøm exponent. The Aerosol extinction coefficient profile at the wavelength λ [nm] in use is then computed via the Ångstrøm law for wavelength dependence:



Page 32 of 79

)(

0λ0 )(),(

zaA

zz ⎟⎠⎞

⎜⎝⎛⋅=

λλκλκ Eq. 24

κ(z, λ) … aerosol extinction coefficient at wavelength in use [km-1] κλ0(z) … aerosol extinction coefficient at reference wavelength [km-1] αA(z) … Ångstrøm exponent [1] λ0 … reference wavelength [nm] λ … wavelength [nm] Computation of aerosol extinction loss:

( )( )

eff),(),(re whe,),(explog10),(

lzzzzL

A

AA

⋅=−⋅−=

λκλτλτλ

Eq. 25

LA(z, λ) … aerosol extinction loss [dB] τA(z, λ) … aerosol optical thickness [1] leff … effective path length [km]; set to 300 km 2.5.2.2 Lowtran based Aerosol Model No constants of List of Constants used. This model works like the SAGE-II based aerosol model with two differences: One difference is that the parameterization of the aerosol extinction coefficient is based on LOWTRAN, referring to Fig.5 in the NOAA ESRL on-line report “Pinatubo effects on the Arctic as derived from airborne and surface observations” (from at http://www.cmdl.noaa.gov, NOAA ESRL GlobalMonitoring Division, Nov 2005). The refer-ence wavelength here is 500 nm and the parameterization is dependent on height (10 height steps between 0 km and 120 km) and distinguishes between background and v

Documents

IRDAS-Report ALPSGuideDocumentation Mar2010 · ESA-IRDAS – ALPS User Guide and Documentation Differential Absorption Spectroscopy in the SWIR for GHG Monito ring using Coherent