aquarius algorithm workshop 18-20 march 2007 college of engineering department of atmospheric,...

Aquarius Algorithm Workshop 18-20 March 2007

College of Engineering Department of Atmospheric, Oceanic & Space Sciences

Chris RufSpace Physics Research Laboratory

Dept. of Atmospheric, Oceanic & Space SciencesUniversity of Michigan

cruf@umich.edu, 734-764-6561 (V), 734-936-0503 (F)

Antenna Sidelobe Correction for Land Contamination

19 Mar 2008 Ruf, Land Contamination, Aquarius Algo Workshop pg 2 of 10

Contributions to Antenna Temperature

TB(Earth in Mainlobe)TB (Earth in Sidelobes) ~ 150K

s2

s1

Parabolic Reflector

Feedhorns

TB(Earth in Mainlobe)TB (Earth in Sidelobes) ~ 150K

s2

s1

Parabolic Reflector

Feedhorns

TB(Earth in Mainlobe)TB (Earth in Sidelobes) ~ 150K

s2

s1

Parabolic Reflector

Feedhorns

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)1(1

cearthSLMBearthSLearthSLAB

cearthSLMBearthSLearthSLMBBA

TTTT

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19 Mar 2008 Ruf, Land Contamination, Aquarius Algo Workshop pg 3 of 10

General Description of Algorithm

• Model TB entering antenna from Earth at all view angels– Derive model from satellite radiometer observations

– Stratify by lat/lon of antenna, obs. frequency, time of year

• Derive sidelobe contribution to TA as antenna pattern weighted average

• Incorporate improved knowledge of sidelobe contribution into standard APC algorithm

19 Mar 2008 Ruf, Land Contamination, Aquarius Algo Workshop pg 4 of 10

Heritage with Other Flight Projects• Obligis, E., L. Eymard and N. Tran, “A new sidelobe

correction algorithm for microwave radiometers: Application to the Envisat instrument,” IEEE Trans. Geosci. Remote Sens., 45(3), 2007.– Use 1 year of Envisat nadir TBs at 23.8 and 36.5 GHz– Stratify by season – 4 time bins– Use nadir TBs directly in antenna pattern weighted averages– Incorporated into Envisat Level 1B operational processing in Nov.

2005• Developed with Jason Microwave Radiometer; Planned for

AMR on OSTM (Jason-2); Shannon Brown lead– Use 3 year JMR nadir TBs at 18.7, 23.8 and 34.0 GHz– Derive model to estimate off-nadir TB from nadir obs by regression of

simulated database of TBs at many angles from ocean/atmos data record and radiative transfer model (over ocean only)

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19 Mar 2008 Ruf, Land Contamination, Aquarius Algo Workshop pg 5 of 10

Brown JMR Results (1 of 3)(ref. Brown, S., “Generate JMR TE Maps,” JPL Tech. Memo, 4 Apr 2006)

Map of the 18.7 GHz nadir brightness temperature centered at LAT=35.5oE, LON=17oN. Inner black circle represents 10o off-nadir. Outer black circle is the Earth limb at 1338 km altitude, approximately 55o off-nadir.

19 Mar 2008 Ruf, Land Contamination, Aquarius Algo Workshop pg 6 of 10

Brown JMR Results (2 of 3)(ref. Brown, S., “Generate JMR TE Maps,” JPL Tech. Memo, 4 Apr 2006)

Earth incidence angle from perspective of 1338 km altitude above ground at LAT=35.5oE, LON=17oN.

19 Mar 2008 Ruf, Land Contamination, Aquarius Algo Workshop pg 7 of 10

Brown JMR Results (3 of 3)(ref. Brown, S., “Generate JMR TE Maps,” JPL Tech. Memo, 4 Apr 2006)

(LEFT) Nadir TB observations at 18.7 GHz(RIGHT) Modeled upwelling TB from perspective of 1338 km altitude above ground at

LAT=35.5oE, LON=17oN. (Note: no change from nadir for land TBs)

19 Mar 2008 Ruf, Land Contamination, Aquarius Algo Workshop pg 8 of 10

Aquarius Sidelobe Land Contribution (1 of 2)(ref. Brown, S., “Aquarius APC,” JPL Aquarius TIM, 1 Feb 2006,)

• Aquarius required to retrieve salinity > 450 km from coast

All points in blue > 450 km from land

19 Mar 2008 Ruf, Land Contamination, Aquarius Algo Workshop pg 9 of 10

Aquarius Sidelobe Land Contribution (2 of 2)(ref. Brown, S., “Aquarius APC,” JPL Aquarius TIM, 1 Feb 2006,)

• Less than 10% of on-Earth sidelobe fraction on land at 450 km (p1V)

(Assumes knowledge of TLand is better than 15 K)

19 Mar 2008 Ruf, Land Contamination, Aquarius Algo Workshop pg 10 of 10

Aquarius Implementation

• Use SMOS observations to train Tearth model– Model for incidence angle dependence of TB over ocean

and land can be better constrained by obs

• Pre-launch simulations– Build Tearth database

– Assess sensitivity of correction to errors in • Integrated antenna beam fractions

• Tearth (seasonal dependence, RFI effects, other?)