1. http://www.eorc.nasda.go.jp/AMSR/ Status of calibration and data evaluation of AMSR on board ADEOS-II Keiji Imaoka a, Yasuhiro Fujimoto a, Misako Kachi a, Toshiaki Takeshima a, Tamotsu Igarashi a, Toneo Kawanishi b, and Akira Shibata a a Earth Observation Research Center, NASDA b ALOS project team, NASDA SPIE International Symposium in Remote Sensing Europe Barcelona, Spain September 8, 2003

2. AMSR TB at all channels (path 11, January 18, 2003) 6V6H10V10H18V18H23V23H36V36H 89AV 89AH 89BV 89BH 50.3V52.8V

3. Characteristics of AMSR Multifrequency, dual-polarized passive microwave radiometer developed by NASDA. Higher spatial resolution compared to existing instruments (e.g., SSM/I). Addition of 6.9-GHz channels for estimating SST and soil moisture, and 50.3 and 52.8GHz for obtaining atmospheric temperature information. Flying in morning orbit (equatorial crossing time: 10:30 am). Combination with AMSR-E on Aqua (1:30 pm) will provide information on diurnal variability. AMSR performing conical scan measurement in orbit. Original ADEOS-II animation can be obtained from NASDA website : http://www.nasda.go.jp/

4. TB images of 50GHz channels 53.6GHz : ~ 4 km 52.8GHz : ~ 1 km No limb correction is necessary. Incidence angle of 55 degrees results in approximately 2 to 3 km of weighting peak. AMSU-A daily browse from http://pm-esip.msfc.nasa.gov/http://pm-esip.msfc.nasa.gov/ First look of 52.8-GHz channel by conically scanning radiometer.

5. AMSR/AMSR-E combination Combination of AMSR-E and AMSR will be a powerful tool to investigate rapidly changing phenomena and diurnal cycle. Cross calibration will be important to keep consistency between AMSR and AMSR-E data. Example of storm tracking by combining AMSR and AMSR-E observations. Processed by using NASDA standard algorithm developed by Dr. Petty (Univ. of Wisconsin-Madison). Rainfall rates are under validation.

6. Characteristics of AMSR Non-deployable, offset parabolic antenna with effective aperture size of 2.0 m. Total power microwave radiometers. High Temperature noise Source (HTS) and Cold Sky Mirror (CSM) for onboard two-point calibration. Two feed horns for 89GHz to keep enough spatial sampling in along track direction. Center Frequency (GHz)6.92510.6518.723.836.550.352.8 89.0 AB Bandwidth (MHz)3501002004001000200400300 PolarizationVertical and HorizontalVerticalVertical and Horizontal 3dB Beam Width (degrees)1.81.20.650.750.350.25 0.15 IFOV (km)40x7027x4614x2517x298x146x10 3x6 Sampling Interval (km)10x105x5 Temperature Sensitivity (K)0.340.7 0.60.71.81.61.2 Incidence Angle (degrees)55.054.5 Dynamic Range (K)2.7 - 340 Swath Width (km)Approximately1600 Integration Time (msec)2.51.2 Quantization (bit)1210 Scan Cycle (sec)1.5

7. Direction of work AMSR and AMSR-E are almost identical instruments in terms of radiometric characteristics. Same problem exists in HTS performance (inhomogeneous physical temperature). Although we have to take into account the differences on thermal condition of the instruments (i.e., different local observing times), which is very important to calibration, direction of calibration activities are almost identical. Base on discussions in course of the examination, the final calibration method may differ from the current approaches.

8. Radiometer sensitivity Time series of radiometric sensitivity while observing HTS (around 300K).

9. Lunar emission in cold cal. Moon sometimes comes insight of CSM view angle and affects the cold calibration counts sometimes up to 30K in 89 GHz due to its small beam size compare to other frequencies. Correction is relatively straightforward since direction of the moon can be computed. After removed the affected counts, simple linear interpolation is applied to fill the gap in L1 processing system. AMSR CSM Output Voltages (March 22, 2003, Path No. 40, Ascending) 06V06H10V10H18V18H23V23H 36V36H50V52H89AV89AH89BV89BH Sample direction (16 points for 89GHz, 8 points for others) Scan direction

10. Earth emission in cold cal. 6.925-GHz CSM counts seem to be affected by Earth’s emission (up to 1K). Our current assumption is that this phenomena is due to a spillover occurring between feed horn and CSM. Earth’s emission pattern is relatively unclear in AMSR case. One possible explanation is a different satellite structure that may intercept the spillover path and obscure the Earth’s emission pattern. AMSR-E AMSR Comparison of the Earth’s emission effect between AMSR-E and AMSR. Psaudo maps are made of 233 and 57 descending paths for AMSR-E and AMSR, respectively.

11. Land emission in cold cal. Correlation was found between variations of contamination and Earth’s Tb of about 110 scans before. L1 processing system subtract this contamination by assuming CSM spillover (spillover occurring between feed horn and CSM) Spillover factor was statistically found and used for correction. Before After Sample images showing the correction. Maps are made of 57 descending paths.

12. Multiple regression model of T eff using eight PRT readings. Coefficients of the regression model were determined by using SSM/I oceanic Tb (18GHz and higher channels) and computed Tb (6 and 10GHz channels) based on the Reynolds OI-SST analysis. SSM/I data were provided by the Global Hydrology Resource Center (GHRC) at the Global Hydrology and Climate Center, Huntsville, Alabama, USA. Reynolds OI-SST dataset were made available by NOAA. Utilize Relationship between receiver temperature and its gain variation. Applying this equation to HTS measurement and assuming T eff derived by regression model as T OBS, b RX can be computed by regression analysis. Using this value, gain variations can be compensated by the equation. Radiometric correction PRT readingsHTS Effective Temp. T OBS : Scene Tb (K) T CSM : Deep space Tb (K) C ’ OBS : Digital counts of scene C ’ CSM : Digital counts of deep spece G 0 : Nominal gain b RX : Gain sensitivity to rec. temp. ( ℃ -1 )  T RX : Rec. temp. departure from mean value ( ℃ ). Step 1 : PRT methodStep 2 : RxT method

13. HTS effective temperature C C OBS CHCH TCTC T OBS THTH SSM/I or simulated Earth Tb HTS Temp. (target) Ta Counts AMSR-E measurement Deep space Temp. Extrapolating HTS effective temperature (target) by using Earth Tb

14. Combining PRT and RxT 23GHz Vpol T b_ HTS & Treciever From PRT method

15. Improvement by adding RxT method BLUE ： HTS effective temp. by PRT method. RED ： HTS effective temp.by PRT+RxT method. RED ： Difference between above two.

16. Radiometric correction 6.925GHz tentative results Comparison between computed Tb based on OI-SST and AMSR Tb by (a) simple two-point calibration and (b) presented method for 6.925-GHz vertical polarization on June 3, 2003. (c) Daily average of difference between computed and AMSR Tb as a function of position in orbit for simple two-point calibration (cross) and presented method (closed circle).

17. Radiometric correction 36.5GHz tentative results Comparison between SSM/I Tb (corrected for difference of incidence angle and center frequency) and AMSR Tb by (a) simple two-point calibration and (b) presented method for 36.5-GHz vertical polarization on June 3, 2003. (c) Daily average of difference between SSM/I Tb and AMSR Tb as a function of position in orbit for simple two-point calibration (cross) and presented method (closed circle).

18. AMSR and AMSR-E comparison It should be noted that AMSR TB are still tentative version.

19. 6.925GHz RFI 6.925GHz vertical polarization, ascending passes (July 8, 2003)

20. Known issues and on-going works Possible overestimation in high Tb over land in 6.925 GHz. Suspect receiver non-linearity characteristics. Need further improvement particularly at lower frequency channels (for SST, etc.). Comparison of 50GHz channels TB with AMSU TB with an incidence angle of near 55 degrees. Utilization of SeaWinds wind speed data to minimize the uncertainties in comparing AMSR TB and computed TB based on Reynolds-SST. Comparison of AMSR and AMSR-E to keep these data set consistent. Assessment of other systematic errors (e.g., scan bias). Assessment of geolocation errors (errors may not be corrected if its size does not exceeds that of AMSR-E).

21. Summary and conclusions AMSR is providing stable data stream since the beginning of normal operation. Same approaches (that were applied to AMSR- E) of post-launch evaluation and calibration are being tested. Some preliminary results of calibration were presented. Our current target date of releasing the data is after 1-year from ADEOS-II launch.

22. AMSR-E data status NASDA/EOC started distribution of AMSR-E L1 brightness temperature (and L3-Tb) products from June 18, 2003. http://www.eoc.nasda.go.jp/amsr-e/index_e.html http://www.eorc.nasda.go.jp/AMSR → AMSR-E Data Release L1A (raw counts) data are also available at NSIDC. http://nsidc.org → Data catalog → AMSR-E/Aqua L1A Raw Observation Counts