Electromagnetics Division

MICROWAVE REMOTE-SENSING PROJECT UPDATE

Presentation to GSICS Microwave Sub-Group, 6 January 2016

David WalkerElectromagnetics Division

NIST, Boulder, CO

Electromagnetics Division

Contributors

• Technical Staff—NIST FTPs

• Kevin Coakley, Statistical Engineering Div.

• Joshua Gordon, RF Electronics Div.

• Mike Janezic, RF Electronics Div.

• David Novotny, RF Electronics Div.

• Jolene Splett, Statistical Engineering Div.

• Technical Staff—NIST Associates

• Dazhen Gu, RA at CU-CET, ECEE Dept.

• Derek Houtz, Ph.D. graduate PREP, CU Aerospace Dept.

• Jim Randa, NIST Retiree

• Jack Surek, NIST contractor

• Chunyue Cheng, Guest Researcher, BIRMM (Beijing)

Electromagnetics Division

Collaborators (partial list)

• Bill Blackwell/Vince Leslie, MIT-LL

• David Draper, Ball Aerospace (Boulder, CO)

• Prof. Bill Emery, CU Aerospace Dept.

• Prof. Al Gasiewski, CU-CET Director, ECEE Dept.

• Ed Kim, NASA GSFC

• Paul Racette, GSFC

• Richard Wylde, Thomas Keating Ltd (UK)

• Axel Murk, Univ. Bern (CH)

Electromagnetics Division

OUTLINE

• Current research topics:

• Brightness-temperature (Tb) standards

• Standard radiometer

• Standard target

• Robotic antenna range (CROMMA facility)

• Advanced radiometer calibration methods

• WR-10 (75 to 110 GHz) radiometer

• Ocean salinity standards

• Summary & plans

Electromagnetics Division

Radiometric Target Measurement

--Use existing NIST radiometer linked to primary noise standards (SI Traceable):

NIST Noise Radiometer + Characterized Antenna

Rad.

Std.

Ant.

Cryo

Amb

C

a

x

0Target

Rad.

Std.

Ant.

CryoCryo

AmbAmb

C

a

x

0TargetTarget

Primary Standards

Electromagnetics Division

Waveguide 6-port reflectometerwith heterodyne receiver

Waveguide banded radiometers

Primary Noise Standards

Electromagnetics Division

Achievable Uncertaintywith Standard Radiometer (only)

Goal is to reach the accuracy requirements for climate change study—data for 18 to 26.5 GHz

NIST

radiometerTroposphere Stratosphere Precipitation

Water

vapor

Sea

surface

temp

u ~ 0.7-1.0 K 0.5 K 1 K 1 K 1.25 K 0.03 K

Ref: “Stability and accuracy requirements for satellite remote sensing instrumentation for global climate monitoring,” ISPRS 2004.

Current coverage: 12 to 65 GHz; soon to include 75 to 110 GHz band (WR-10)

Electromagnetics Division

Transfer NIST Tb cal to instrument radiometer

antenna

anechoic chamber

targetNISTRadiometer

antenna

anechoic chamber

targetInstrumentRadiometer

Note: Geometry mustbe maintained in xfer

Transfer pre-launch cal to on-orbit cal: background change can be accommodated

antennatargetInstrument

Radiometer

SpaceEnvironment

Electromagnetics Division

Black Body Targets--Current DesignConstrained volume and mass for space and

aircraft calibration

large temperature gradients

Up to 0.6 K mean offset from recorded temp

Narrow optimal operating frequency range due to periodic pyramid structure

0 0.01 0.02 0.03 0.04 0.050

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.09

z (m)

r (m

)

346.5

347

347.5

348

348.5

349

349.5

Cox, A.E. et al. “Initial Results from the Infrared Calibration and Infrared Imaging of a Microwave Calibration Target” Int. Geoscience and Remote Sensing Symposium, Denver 2006.

Gu, Dazhen. “Reflectivity Study of Microwave Blackbody Targets” Trans. on Geoscience and Remote Sensing, vol. 49, No. 9, Sept. 2011.

Electromagnetics Division

NIST BB Standard Target Design

Single open conical structure

Uniform emissivity ≈ 1 over broad microwave frequency spectrum (10-200 GHz)

Minimal temperature gradients

Operating temperature range: 80 K to 350 K

heat exchanger tubing

conductive base

layered microwave absorber

foam insulation

Electromagnetics Division

Std Target--Thermal Modeling• Physical T of BB design simulated with CFD software

• TVAC as well as ambient environment

• Thin polyethylene foam insulating layer necessary even in vacuum

ANSYS 3D finite element solution 2D heat equation solution of cross section

simulated streamlines in anechoic chamber (left) and resulting temperature contour with 3 mm insulation layer (right)

Electromagnetics Division

Electromagnetic Modeling• Optimized absorber layer solution input to full wave

finite element electromagnetic solver (HFSS*)

• Emissivity derived from reflectance distribution

• ~1 hour/frequency point running on 16-processor 130 GB RAM HPC

-80

-75

-70

-65

-60

-55

-50

-45

-40

90 100 110 120 130 140 150 160 170 180

Ref

lect

ance

(d

B)

θ (deg)

Reflectance from Normal Incidence Excitation - f = 51.76 GHz

Phi = 0 Phi = 45 Phi = 90

Electromagnetics Division

TB and Uncertainty Calculation• Calculate effective brightness temperature from physical temperature,

electromagnetic blackbody reflectivity, and antenna pattern simulations

• 350 K set temperature

• U calculation by Monte Carlo simulation including:

• Mat’l parameter U

• EM simulation convergence error

• CFD simulation error

• Total u = ~0.05 K

• U (k=2) = ~ 0.1 K

20 40 60 80 100 120 140 160 180349.92

349.94

349.96

349.98

350

350.02

350.04

350.06

Frequency (GHz)

Eff

ective B

lackbody B

rightn

ess T

em

pera

ture

(K

)

Electromagnetics Division

BB Standard Target—Status• Design finalized FY15 with ε and u(T) goals met

• Contract let to Thomas Keating, Ltd.

• 2 targets: 23 cm and 13 cm apertures, to match ATMS requirements

• Absorber test samples being measured to confirm model-fabrication compatibility

• Target fabrication will include absorber “witness samples” to verify EM performance

• Estimated completion: September 2016

Electromagnetics Division

Transfer NIST BB Tb std to instrument radiometeranechoic chamber

BB

antennaInstr.target

InstrumentRadiometer

Transfer pre-launch cal to on-orbit cal: background change can be accommodated

antennatargetInstrument

Radiometer

SpaceEnvironment

antennaInstrumentRadiometer

anechoic chamber

Compare/Calibrate instrumentcal target(s) with NIST BB std

Electromagnetics Division

WR-10 Radiometer• WR-10 cryogenic noise standard:

• W. C. Daywitt, “Design and Error Analysis for the WR10 Thermal Noise Standard,” NBS Technical note 1071, Dec. 1983.

• Similar architecture to other NIST noise radiometers, with 2 separate IF chains

• Component evaluation and subassemblies under construction

• Est. completion Dec. 2016

TDUT

TRT

TCT

LPF44dB

12.5 to 18.33 GHz

active

x6 chain

IF out

25 to 36.67 GHz IF out

30dB

test

0

0.005

0.01

0.015

0.02

75 80 85 90 95 100 105 110

Gigahertz

-14

-12

-10

-8

-6

-4

-2

0

2

75 80 85 90 95 100 105 110

LO [dBm]

RF [dBm]

Conversion Loss [dB]

Gigahertz

WR-10 Radiometer Circuit schematic

WR-10 Cryogenic Standard |S11|

Balanced Mixer Conversion Loss

Electromagnetics Division

Summary & Plans• TB standard radiometer

• Initial development 18-26.5 GHz band; 12 to 65 GHz now, with 75-110 GHz radiometer in 2017

• Demonstrate practical cal. transfer to flight instrument

• Primary standard target

• Significant reduction in uncertainty—U ~ 0.1 K)

• Provides a means for Tb transfer & verification

• Modeling & design completed

• Fabricate & test target FY16-17

• Ocean salinity

• Resonant cavity for L-band under construction

• Sea water traceable measurements in FY17

• Robotic antenna range (CROMMA) operational

• “Millimeter-Wave Near-Field Measurements Using Coordinated Robotics,” Gordon, J.A.; Novotny, D.R.; Francis, M.H.; Wittmann, R.C.; Butler, M.L.; Curtin, A.E.; Guerrieri, J.R., IEEE Trans. Antennas and Propagation, 2015, Volume: 63, Issue: 12, Pages: 5351 - 5362, DOI: 10.1109/TAP.2015.2496110