Aquarius Algorithm Workshop 18-20 March 2007

1. College of Engineering Department of Atmospheric, Oceanic & Space Sciences Aquarius Algorithm Workshop 18-20 March 2007 Antenna Sidelobe Correction for Land Contamination Chris Ruf Space Physics Research Laboratory Dept. of Atmospheric, Oceanic & Space Sciences University of Michigan cruf@umich.edu, 734-764-6561 (V), 734-936-0503 (F)

2. Contributions to Antenna Temperature

3. 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

4. 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)

5. 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.

6. 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.

7. 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)

8. 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

9. 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)

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?)