| Paper: | FR-A1.6 |
| Session: | Instruments and Calibration (Posters) |
| Time: | Friday, March 30, 09:00 - 10:20 |
| Presentation: |
Poster
|
| Topic: |
Advanced radiometer techniques: |
| Title: |
Estimation of NPP/JPSS ATMS Antenna Emission from Cold Space Observations |
| Authors: |
Hu (Tiger) Yang; University of Maryland | | |
| | Quanhua (Mark) Liu; NOAA | | |
| | Ninghai NOAA Affiliate; NOAA | | |
| | Kent Anderson; NGES | | |
| Abstract: |
The Advanced Technology Microwave Sounder (ATMS) onboard the Suomi National Polar-orbiting Partnership (NPP) satellite and JPSS satellite is a total power radiometer and scans across the track within a range of ±52.77° from nadir. It has 22 channels and measures the microwave radiation at either quasi-vertical or quasi–horizontal polarization from the Earth’s atmosphere. ATMS scanning reflector is made of the beryllium coated with gold and can have an emission due to the surface roughness. An estimate of the reflector emissivity in the prelaunch phase was not explored. The study of reflector emissivity characteristic for NPP and J1/N20 ATMS antenna is an important part of NPP/JPSS on-orbit calibration evaluation tasks. ATMS antenna reflector can emit the radiation due to the coating material and surface roughness and have an impact on calibration accuracy. Its cross-track rotation can complicate its emission problem by changing the polarization state of incident wave. Since its reflection coefficient is close to one and it is difficult to measure the antenna emission at ground. Thus, we develop a technique to estimate the ATMS plane reflector emission for frequency ranging from K to W bands. Using the Mueller matrix of reflection and transmission at 45o angle for a bulk-material reflector, we derived a full vector expression for reflected radiation for non-lossless, polarized rotating reflector. The physical model is then applied to the two-point calibration equation and the antenna emissivity can be derived from the pitch-over observations. For NPP ATMS, the reflector emissivity spectrum ranges from 0.002 to 0.006 from K to G bands. Error model are also developed to assess the impacts of antenna emissivity to calibration. Results show that the calibration error can be as large as 2.5K for space view at channel 16. The error is scene dependent and different for different channel of ATMS due to the nonlinearity characteristic at each channel. For unpolarized channels the scan dependent feature of TDR error is dominated by sine square term at quasi-V channels and cosine square term in quasi-H channels. For polarized window channels, the impacts of antenna emissivity to observed scene brightness temperature are complicated by the rotation of polarization state, which will be studied in our future work. |
