Abstract
The Advanced Technology Microwave Sounder (ATMS) is one of five instruments on the Suomi National Polar Partnership (S-NPP) satellite, launched in 2011. A second ATMS, nearly identical to S-NPP ATMS but with different receiver front-end electronics, will be hosted on the Joint Polar Satellite System (JPSS1, 2017 launch) and has recently completed thermal vacuum (TVAC) calibration testing. ATMS noise is measured in a number of ways during TVAC testing to assess the power spectral density and the noise correlation among different channels. An important finding of these tests is that the spectral and correlation structure of ATMS noise is markedly different than on AMSU-A, with ATMS generally exhibiting lower white noise but higher colored (1/f) noise. Another artifact of the 1/f noise is higher interchannel correlation (Kim, 2014). These differences have been attributed at least in part to gain fluctuations of amplifiers in the receiver systems, whether from new RF LNA MMICs in the receiver architecture or RF LNA MMICs that are fabricated with different materials and smaller gate lengths.
Recent work has evaluated the impact of the ATMS noise characteristics on Numerical Weather Prediction (NWP) (Bormann, Fouilloux, & Bell, 2013). Interchannel correlation and brightness temperature image striping due to 1/f noise appear to degrade assimilation performance, so there is therefore a strong motivation to carefully characterize the noise processes (discussed in this talk) and further optimize both the numerical assimilation models and methods. There may also be implications for the design of future sounding instruments.
This presentation will provide analysis of the ATMS noise spectra and correlation coefficients to characterize the 1/f noise and interchannel correlation for both the JPSS1 and S-NPP builds. This will help develop potential instrument requirements to mitigate 1/f noise and therefore interchannel correlation, and gain experience with the impact of the 1/f noise inside the calibration algorithm. The noise spectra will be divided into the 1/f and thermal noise contributions. The characterization will also follow the interchannel correlation through the various stages of the typical periodic absolute calibration algorithm used by ATMS and heritage instruments. The analysis uses the pre-launch data when ATMS was in a thermal vacuum chamber and viewing external precision calibration targets.
Bormann, N., Fouilloux, A., & Bell, W. (2013). Evaluation and assimilation of ATMS data in the ECMWF system. Journal of Geophysical Research: Atmospheres, 118, 12,970-12,980.
Kim, E. et al. (2014). S-NPP ATMS Instrument Pre-Launch and On-Orbit Performance Evaluation. Journal of Geophysical Research: Atmospheres, 119.
This work is sponsored by the National Oceanic and Atmospheric Administration under Air Force Contract FA8721-05-C-0002. Opinions, interpretations, conclusions, and recommendations are those of the authors and are not necessarily endorsed by the United States Government.
S-NPP and J1 ATMS Noise Spectral and Correlation Analysis using Pre-launch Data
The Advanced Technology Microwave Sounder (ATMS) is one of five instruments on the Suomi National Polar Partnership (S-NPP) satellite, launched in 2011. A second ATMS, nearly identical to S-NPP ATMS but with different receiver front-end electronics, will be hosted on the Joint Polar Satellite System (JPSS1, 2017 launch) and has recently completed thermal vacuum (TVAC) calibration testing. ATMS noise is measured in a number of ways during TVAC testing to assess the power spectral density and the noise correlation among different channels. An important finding of these tests is that the spectral and correlation structure of ATMS noise is markedly different than on AMSU-A, with ATMS generally exhibiting lower white noise but higher colored (1/f) noise. Another artifact of the 1/f noise is higher interchannel correlation (Kim, 2014). These differences have been attributed at least in part to gain fluctuations of amplifiers in the receiver systems, whether from new RF LNA MMICs in the receiver architecture or RF LNA MMICs that are fabricated with different materials and smaller gate lengths.
Recent work has evaluated the impact of the ATMS noise characteristics on Numerical Weather Prediction (NWP) (Bormann, Fouilloux, & Bell, 2013). Interchannel correlation and brightness temperature image striping due to 1/f noise appear to degrade assimilation performance, so there is therefore a strong motivation to carefully characterize the noise processes (discussed in this talk) and further optimize both the numerical assimilation models and methods. There may also be implications for the design of future sounding instruments.
This presentation will provide analysis of the ATMS noise spectra and correlation coefficients to characterize the 1/f noise and interchannel correlation for both the JPSS1 and S-NPP builds. This will help develop potential instrument requirements to mitigate 1/f noise and therefore interchannel correlation, and gain experience with the impact of the 1/f noise inside the calibration algorithm. The noise spectra will be divided into the 1/f and thermal noise contributions. The characterization will also follow the interchannel correlation through the various stages of the typical periodic absolute calibration algorithm used by ATMS and heritage instruments. The analysis uses the pre-launch data when ATMS was in a thermal vacuum chamber and viewing external precision calibration targets.
Bormann, N., Fouilloux, A., & Bell, W. (2013). Evaluation and assimilation of ATMS data in the ECMWF system. Journal of Geophysical Research: Atmospheres, 118, 12,970-12,980.
Kim, E. et al. (2014). S-NPP ATMS Instrument Pre-Launch and On-Orbit Performance Evaluation. Journal of Geophysical Research: Atmospheres, 119.
This work is sponsored by the National Oceanic and Atmospheric Administration under Air Force Contract FA8721-05-C-0002. Opinions, interpretations, conclusions, and recommendations are those of the authors and are not necessarily endorsed by the United States Government.