| Paper: | FR-P1.6 |
| Session: | Instrument Calibration I |
| Time: | Friday, March 30, 15:00 - 15:20 |
| Presentation: |
Oral
|
| Topic: |
Sensor calibration: |
| Title: |
Soil Moisture Active/Passive (SMAP) L-band Microwave Radiometer Post-Launch Calibration Upgrade |
| Authors: |
Jinzheng Peng; NASA Goddard Space Flight Center / Universities Space Research Association | | |
| | Sidharth Misra; NASA Jet Propulsion Laboratory | | |
| | Jeffrey Piepmeier; NASA Goddard Space Flight Center | | |
| | Emmanuel Dinnat; NASA Goddard Space Flight Center / Chapman University | | |
| | Simon Yueh; NASA Jet Propulsion Laboratory | | |
| | Thomas Meissner; Remote Sensing Systems | | |
| | David Le Vine; NASA Goddard Space Flight Center | | |
| | Kacie Shelton; NASA Jet Propulsion Laboratory | | |
| | Adam Freedman; NASA Jet Propulsion Laboratory | | |
| | R. Scott Dunbar; NASA Jet Propulsion Laboratory | | |
| | Rajat Bindlish; NASA Goddard Space Flight Center | | |
| | Steven Chan; NASA Jet Propulsion Laboratory | | |
| | Giovanni De Amici; NASA Goddard Space Flight Center | | |
| | Priscilla N Mohammed; NASA Goddard Space Flight Center / Morgan State University | | |
| | Liang Hong; NASA Goddard Space Flight Center / Science Application International Corporation Headquarters | | |
| | Derek Hudson; NASA Goddard Space Flight Center | | |
| | Thomas Jackson; USDA ARS Hydrology and Remote Sensing Laboratory | | |
| Abstract: |
The SMAP mission’s observatory was launched on 31st January 2015 in a 6 AM/ 6 PM sun-synchronous orbit at 685 km altitude to measure soil moisture and freeze/thaw globally. The SMAP radiometer L1B data product version 3 has been released for public science activities, and the post-launch calibration and validation activities for the version 3 data product are published/reported. Validation after the update to the thermal model for the reflector shows that: (1) There is calibration drift over global ocean during eclipse seasons, and (2) There is a 2.6 K bias compared to the celestial Cold Sky (CS). Inter-comparison of land brightness temperature (TB) between SMAP and SMOS (Soil Moisture and Ocean Salinity) shows that SMAP land TB is 2.7 K colder. Due to the calibration drift and bias, the SMAP radiometer is under re-calibration for the next data release in 2018.
The SMAP radiometer still uses the global ocean and CS as the primary external calibration targets. In the previous calibration approach the antenna gain and the noise diode’s equivalent noise temperature were calibrated in sequence and the reflector emissivity was reset to its value with the update of the reflector’s thermal model. In the approach for the next data release, the calibration is being upgraded to compute the three calibration parameters (the equivalent noise temperature of the noise diode, the offset of the reference load, and the antenna gain) jointly by using the global ocean and CS with both 110o and 180o pitch maneuvers as references. This will be done after the reflector’s emissivity (or loss factor) is established. Three different approaches have been used to compute the reflector’s emissivity, and the results agree well and all of them are much larger than the baseline value.
During the calibration, three ocean roughness models including the Geophysical Model Function model used for SMAP winds are compared. The modeled TBs for vertical polarization (V-pol) agree well, but the modeled TBs for horizontal polarization (H-pol) have larger disagreement. A special orbit maneuver was implemented in which there was enough nadir-looking time over both ocean and land to evaluate any potential bias in the modeled antenna temperature of H-pol. The result was used to adjust the modeled H-pol antenna temperature over the external calibration targets for the post-launch calibration.
The uncertainties in the three calibration parameters are then solved, and the L1B data using the new calibration coefficients have been generated for testing and evaluation of the performance of the upgraded calibration algorithm. The data show that both calibration drift during eclipse season and bias over CS are removed. The RMSDs (root mean square deviation) of the calibration drift over both the global ocean and CS are less than 0.1 K. Comparing to the L1B version 3 data, the land TBs for the next data release are increased by 2.9 K for V-pol and 3.3 K for H-pol. Additional validation activities are in progress and the results will be presented in the conference. |
