The Inter-Calibration of AMSR-E with WindSat, F13 SSM/I, and F17 SSM/IS Frank J. Wentz Remote Sensing Systems 1 Presented to the AMSR-E Science Team June 28, 2011 NCDC, Asheville, NC

The Problem Volume: Nearly 100 satellite-years of observations from Microwave Radiometers. Calibration : Each sensor has its own unique set of Sensor Calibration Problems Precision: High precision required for Climate Studies Satellite Microwave Radiometers

3 Satellite Calibration Methodology

4 F13 SSM/I, F17 SSM/IS, AMSR-E, and WindSat have been finalized at the RSS V7 Calibration Standard: Both TA/TB and Geophysical Products SST, wind, vapor, cloud, and rain have been thoroughly validated  Direct In Situ Comparisons  Inter-satellite Comparisons  A very large number of research studies Geophysical products, including rain, are consistent across all platforms Geophysical Products Radiative Transfer Model Simulated Antenna Temperature Measured Antenna Temperatures TA Anomaly Statistics Satellite Calibration Methodology Final Step

Port Symmetry WindSat 10.7 GHz Global TA(v) versus TA(h) TA(v) ≈T(h) over hot land: Indicate that η V = η h 5 ocean land 0 K V-pol T A 350 K 0 K H-pol T A 350 K

6 Absolute Errors in Hot Load and Spillover are Equivalent Simplified TB equation (cold space and cross-pol set to 0) Change in TB due to errors in specifying hot load temperature and spillover  Hot-Load/Spillover error dominates absolute calibration error  Typical values for past satellites is 1 to 2 K (previous table)  GMI Specification is 1.35 K  RSS post-launch calibration assumes this error is the same for both polarizations with a few exceptions.

7 7 GHz11 GHz19 GHz23 GHz37 GHz90 GHz F F F AMSR-E WindSat Standard Rules Applied to All Sensors: 0.3 K added to Planck cold space value (except JAXA added 0.7 K for AMSR-E) 1.0 K subtracted from thermistor hot load readings RSS derived Spillover minus pre-launch value reported by NRL or JAXA Spillover difference multiplied by 200 K to show typical TB difference in Kelvin Color Coding: +2K Absolute Calibration: Spillover

8 7 GHz11 GHz19 GHz23 GHz37 GHz90 GHz F F F AMSR-E WindSat RSS derived Cross-Pol minus pre-launch value reported by NRL or JAXA Spillover difference multiplied by 50 K to show typical TB difference in Kelvin Color Coding: 0.5K Absolute Calibration: Cross-Pol A compelling validation of the radiative transfer model GMI has extremely small cross-pol  precise RTM validation

9 A One-Parameter Absolute Calibration Model For each frequency, one tuning parameter is required to match the brightness temperature observations to the RTM. This single parameter is sufficient for both polarizations and for both ocean and land and presumably sea ice and snow. This tuning parameter accounts for the combined knowledge error of the effective hot load temperature and spillover The magnitude of this parameter is K.

10 A One-Parameter Absolute Calibration Model Caveats 1.For fine turning, we do make small (0-0.3K) adjustments to cross-pol. 2.For 3 cases out of 23, we find a polarization difference in spillover: AMSR-E 23.8 GHz K AMSR-E 89.0 GHz K F17 SSM/I91.7 GHz K All 3 cases show this polarization anomaly over both ocean and land 3.The RSS RTM is used as the Reference. Note however that when averaged over the ensemble of MW sensor, the absolute calibration adjustments are close to zero 4.There are relative adjustments that are made that are functions of scan position and sun angles Note however these adjustments are all bias neutral.

11 7 GHZ, Hpol11 GHZ, Hpol 19 GHZ, Hpol23 GHZ, Hpol 37 GHZ, Hpol89 GHZ, Hpol Mission TA Anomaly Plots AMSR-E Problem at 19 GHz

12 7 GHZ, Hpol11 GHZ, Hpol 19 GHZ, Hpol23 GHZ, Hpol 37 GHZ, Hpol89 GHZ, Hpol WindSat (750 MHz) AMSR-E (200 MHz) AMSR-E Adjusted Mission TA Anomaly Plots 60 Megahertz change to AMSR-E 18.7 GHz channel

13 7 GHZ, Hpol11 GHZ, Hpol 19 GHZ, Hpol23 GHZ, Hpol 37 GHZ, Hpol89 GHZ, Hpol 13 Mission TA Anomaly Plots AMSR-E Cloud-Crosstalk Problem

14 Location of Persistent Clouds

15 Problem with Cloud Cross-Talk In Vapor Retrieval Algorithm

16 7 GHZ, Hpol11 GHZ, Hpol 19 GHZ, Hpol23 GHZ, Hpol 37 GHZ, Hpol89 GHZ, Hpol 16 Mission TA Anomaly Plots AMSR-E Cloud-Crosstalk Problem

17 7 GHZ, Hpol11 GHZ, Hpol 19 GHZ, Hpol23 GHZ, Hpol 37 GHZ, Hpol89 GHZ, Hpol Mission TA Anomaly Plots AMSR-E Cloud-Crosstalk Removed

18 Conclusions Proper calibration requires that one starts with the raw radiometer counts and then apply consistent methods and algorithms to all sensors. Major sources of calibration error are: 1.Specification of antenna spillover and mean hot load temperature 2.Specification of the variation of hot load temperature with varying sun angles 3.Emissive antenna correction (TMI and SSM/IS) There are many minor sources of calibration error 1.Small Cross-Pol Adjustments 2.Along-scan biases 3.Moon in Cold mirror 4.Etc. The RSS V7 Calibration Standard is a highly evolved RTM that is applied to all satellite sensors. AMSR-E, WindSat, F13 SSM/I and F17 SSM/IS are now at the RSS V7 Calibration Standard. The remaining SSM/I will soon follow.