| Paper: | FR-A1.4 |
| Session: | Instruments and Calibration (Posters) |
| Time: | Friday, March 30, 09:00 - 10:20 |
| Presentation: |
Poster
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| Topic: |
Advanced radiometer techniques: |
| Title: |
DEVELOPING VICARIOUS CALIBRATION FOR MICROWAVE SOUNDING INSTRUMENTS USING LUNAR RADIATION |
| Authors: |
Hu (Tiger) Yang; University of Maryland | | |
| | Quanhua (Mark) Liu; NOAA | | |
| | Ninghai Sun; NOAA | | |
| | Kent Anderson; North Grumman Electronic System | | |
| | Idahosa Osaredin; Massachusetts Institute of Technology | | |
| | Robert Leslie; Massachusetts Institute of Technology | | |
| Abstract: |
Accurate global observations from space are critical for global climate change study. However, atmospheric temperature trend derived from space-borne microwave instruments remains a subject of debate, due mainly to the uncertainty in characterizing the long-term drift of instrument calibration. Thus, a highly stable target with a well-known microwave radiation is required to evaluate the long-term calibration stability. This study develops a new model to simulate the lunar emission at microwave frequencies and the model is then used for monitoring the stability of the Advanced Technology Microwave Sounder (ATMS) onboard Suomi NPP satellite. It is shown the ATMS cold space view of lunar radiation agrees well with the model simulation during the past five years and this instrument is capable of serving the reference instrument for atmospheric temperature trending studies, and connecting the the previous generation of microwave sounders from NOAA-15 to the future JPSS microwave sounder onboard NOAA-20 satellite.
It is found that for high frequency channels with smaller FOV size, the lunar model performance is largely determined by the accuracy of lunar solid angle calculated from ground measured antenna pattern. Sensitivity of lunar simulation model to antenna beam solid angle is beam width dependent: A 10% uncertainty of beam solid angle in lower frequency channel with FOV size of 5.2o can only raise a 0.13K model simulation bias, while it will introduce as large as 3K biases in channels with 1.1o beam width. From antenna pattern ground measurements for SNPP and JPSS-01 ATMS we learned that the uncertainty in antenna beam solid angle in ATMS G bands is larger than 10%. This might explain the lunar model error in G found. Therefore accurate information of antenna beam solid angle is very important for successful implementation of the lunar model developed in this paper.
As demonstrated in this work, a reliable lunar Tb model can be established from a well calibrated ATMS, combined with accurate ground measurements of antenna pattern. Therefore in future it is possible to obtain the warm load equivalent effective lunar brightness temperature for calibration by using a finer beam width in lunar observations. This is especially important for on-orbit calibration of small and cubic satellites.
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