A GNSS-R DEMONSTRATION MISSION FOR SEA STATE … · • GNSS-Reflectometer operated while receiver is connected to the antenna, • Combination of up-looking and down-looking channels

IGARSS 2011, Vancouver, Canada, July 25-29, 2011 © UPC, ADTelecom 2011 1

PAU INSTRUMENT ABOARD INTA MICROSAT-1:

A GNSS-R DEMONSTRATION MISSION FOR SEA STATE CORRECTION IN L-BAND RADIOMETRY

A. Camps1, J.F. Marchán1,5, E. Valencia1, I. Ramos1, X. Bosch-Lluis1, N. Rodriguez1, H. Park1, A. Alcayde2, S. Chavero2, P. Martínez2, A. Mollfulleda2, J. Galindo2, M. Angulo3, and A. Rius4

1Dept. of Signal Theory and Communications, Universitat Politècnica de Catalunya and IEEC CRAE/UPC, UPC Campus Nord, D4-016, 08034 Barcelona, Spain. E-mail: [email protected]

2ADTelecom, Camí de la Pelleria, 12, P.I. Bonavista, 08915 Badalona, Spain 3INTA, Dept. Progrs. Espaciales y Ciencias del Espacio, Torrejón de Ardoz 28850, Madrid, España 4IEEC/ICE-CSIC, Campus UAB/Fac. Ciències, Torre C-5-parell-2a planta, 08193 Bellaterra, Spain

5Institut Cartogràfic de Catalunya, Parc de Montjuïc, 08038 Barcelona, Spain


Outline of the presentation:

1. Introduction

2. Measurement Concept

3. Instrument Heritage

4. PAU in INTA’s MicroSat-1

5. Preliminary Tests

6. Conclusions


• L-band microwave radiometry is the best suited for Sea Surface Salinity and Soil Moisture e.g.: SMOS, Aquarius, SMAP missions

• The brightness temperature of the sea surface depends on:

- salinity - physical temperature - sea state (surface roughness)

critical correction: . SMOS: aux. data + multi-angular information . AQUARIUS: L-band scatterometer

• Potential solution = combination in a single instrument 3 different sensors:

- PAU-RAD: New type of radiometer measure TB - PAU-GNSS/R: GPS reflectometer measure sea state (and altimetry) - PAU-IR: IR radiometer measure SST

(PAU concept proposed to ESF in 2003, granted in 2004, cont’ MICIIN projects)

1. Introduction

, , ,,SST,SSS 1 , , SSST S, ,SS S Trh v h v h vT pT f aram


• GNSS opportunity signals reflected over the sea

surface come from a larger area (“glistening zone”)

when the sea is rough longer delays as compared

to specular reflection point + larger Doppler shifts

• The Delay Doppler Map (DDM) provides an indication of the “widening”

of the so-called glistening zone

related to TB may be used to correct for sea state

2. Measurement Concept

• Sample DDMs from UK-DMC (Tcoh.= 1 ms; Tincoh. = 200 ms) over the ocean, land and ice

IGARSS 2011, Vancouver, Canada, July 25-29, 2011 © UPC, ADTelecom 2011

3. PAU Instrument Heritage (i) griPAU ground-based instrument (Gran Canaria, 2008 & 2009) sea state determination and impact on TB • 24x32 DDM points (min =0.09 chips, fd=200 Hz) • Tcoh. min = 1 ms / Tcoh. max = adjustable • Tincoh. min = 1 ms / Tincoh. max = adjustable

DO-DEREC early tests (July 2002) 40 km South of Barcelona

PAU-ORA (One Receiver Airborne): ALTIMETRIC & SM applications

5


3. PAU Instrument Heritage (ii) TB Sensitivity to Normalized DDM Volume

TB Sensitivity to Waveform’s Tail Length

6

0.51

1.52

2.5

-2000-1000

01000

2000

1

2

3

x 105

Delay [chips]

Measured DDM and threshold applied

Doppler [Hz]

[au]

0.5

1

1.5

2

2.5

x 105


4. PAU in INTA’s MicroSat-1 (i): Sponsored by Spanish Ministry of Science and Innovation “Sistemas GNSS-R para Futuras Misiones SMOS: SUBPROYECTO UPC”, code: AYA2008-05906-C02-01/ESP


UP-looking antenna

DOWN-looking antenna

Processing

board #2

Processing

board #1

UP-looking antenna

DOWN-looking antenna

Processing

board #2

Processing

board #1

Simplified design: • Radiometer operated as a TPR with frequent calibration, • GNSS-Reflectometer operated while receiver is connected to the antenna, • Combination of up-looking and down-looking channels through coupler Frequency plan: • fRF = 1575.42 MHz, fIF = 70 MHz, fs = 16.384 MHz Architecture: • Two cold redundant receivers and processing boards.

4. PAU in INTA’s MicroSat-1 (ii):


1. Antenna array optimized for lowest possible ohmic losses and maximum gain Planar structure (microstrip patches + stripline 8:1 power combiner < 6 mm thick)

4. PAU in INTA’s MicroSat-1 (iii): Antenna Array Design

Patch GPS R4360

f= 1575.42 MHz

r = 6.15

l = 36.6 mm

h = 2.54 mm

S11 = -25 dB

G = 5.37 dB

= 86%

Array

G = 15 dB


4. PAU in INTA’s MicroSat-1 (iv): All boards (Engineering Model – final version pending)

RF

BOARD

DPU

MAIN

BOARD

VOLTAGE

SUPPLY

BOARD

10


4. PAU in INTA’s MicroSat-1 (v): RF/IF chain 2. RF / IF chain to provide G ~ 110 dB gain, NF ~ 2 dB, B ~ 2.2 MHz

G [dB]

Gcum [dB]

IP3 [dB]

IP3cum [dB]

NF [dB]

NFcum [dB]


4. PAU in INTA’s MicroSat-1 (vi): DPU

3. Signal Processor

• Virtex-4 FPGAs + in-orbit reconfiguration capability

• Interfaces: CAN (commands & reconfigurability), Space-Wire (data)

• DDM size: 4096* samples in delay x 16 samples in Doppler

• “Dummy” processing: Sequential search of all GPS satellites using

1 ms coherent integration time + > 10 incoherent avg. (100 typ.)

• On-board NRT processing or raw data acquisition


SpaceWire

Interface

CAN

interface

FPGA

SRAM

ADC

Back-

panel

connector

IF

Input

signal

PROM

CLOCK

GENERATION

Data Processing Unit Main Board (x 2: space-qualified + commercial compts.)

4. PAU in INTA’s MicroSat-1 (vii): DPU


4. PAU in INTA’s MicroSat-1 (viii): Boards being stacked


4. PAU in INTA’s MicroSat-1 (ix): Boards being stacked


5. Preliminary Tests: (i)

R&S SMU-200A arbitrary signal

generator + GPS module Acquisition Set-up

16


Sampling = 6-bit

Level = GPS L1 C/A at ground level

Tcoh =1 ms

Nincoh =1

Delay [lags]

fDoppler

[Hz]

5. Preliminary Tests: (ii)

Delay [lags]

Doppler [lags]


Sampling = 6-bit

Level = GPS L1 C/A at ground level -15 dB

Tcoh = 2 ms

Nincoh =50

Delay [lags] Doppler [lags]

5. Preliminary Tests: (iii)


• PAU in INTA MicroSat-1 is a small secondary payload to test sea state correction in L-band radiometric observations (TB vs Volume under the normalized DDM). • Combination of direct and reflected signals will allow also to “explore” other scatterometric and altimetric measurements • Planar antenna size limited by available space: trade-off between low ohmic losses (~86%), “high” gain (~15 dB), side lobes (-11 dB at 90º), mass and thickness (< 6 mm). • Computes real-time DDMs or stores raw data for ground processing • Engineering Model finished and first tests performed. • Current basic processing scheme: Tcoh = 1 ms, Nincoh. avg = 100 + blind sequential search of GPS satellites in view

6. Conclusions


Acknowledgements:

Activities sponsored by ESF – EURYI 2004 grant and the Spanish Ministry

of Science and Innovation “Sistemas GNSS-R para Futuras Misiones

SMOS: SUBPROYECTO UPC”, code: AYA2008-05906-C02-01/ESP

Documents

A GNSS-R DEMONSTRATION MISSION FOR SEA STATE … · • GNSS-Reflectometer operated while receiver is connected to the antenna, • Combination of up-looking and down-looking channels