Preparing for JPSS-1/ATMS Direct Readout Readiness

1. Preparing for JPSS-1/ATMS Direct Readout Readiness • Nikisa S. George & Kent Anderson • Northrop Grumman Electronic Systems, Azusa CA, 91702, U.S.A. • Overview • The Advanced Technology Microwave Sounder (ATMS), manufactured by Northrop Grumman Electronic Systems (NGES) in Azusa CA, was launched on October 28, 2011 aboard the Suomi National Polar-orbiting Partnership (NPP) spacecraft • ATMS works in conjunction with the Cross-track Infrared Sounder (CrIS) to measure atmospheric temperature and humidity profiles and is the follow-on to the Advanced Microwave Sounding Units -A and -B • The next ATMS, currently in system-level testing, will be on the Joint Polar Satellite System-1 (JPSS-1), planned for launch in 2017 • This study reviews: • Our performance assessments from Cal-Val activities • Scan-dependent radiometric biases and “striping” • Preliminary algorithm options that may be useful for direct readout users • “Striping” Noise • “Striping” is due to scan-to-scan (down-track) variations that are greater than sample-to-sample variations within a scan (cross-track) (see Figure 4) • No requirement has yet been established, but it is now recognized that such a requirement needs to be developed • Phenomenon is due to low-frequency gain fluctuations, predominantly in front-end LNAs • Associated issue of multi-channel correlation of gain fluctuations is also under investigation • Summary of NPP On-orbit Assessments • Radiometric Sensitivity: Channels 1-16 reduced by 1/3, for direct comparison to AMSU-A (Figure 2a) • Radiometric Accuracy:Analytic model, with parameter updates based on On-orbit Data (Figure 2b) a) Feb 20, 2012 - ATMS Pitch Maneuver; Ch 3 in Kelvin Cross Track Beam Position b) Down Track Scan Figure 4. ATMS Striping example • ATMS Description • Total-power radiometer, two-point external calibration • Continuous cross-track scanning • Functional-equivalent follow-on to AMSU-A and MHS, with improved sampling and coverage • Potential Algorithm Options for JPSS • Corrections for the scan-dependent bias, based on modeled effect of reflector emissivity • Multi-channel processing to reduce correlated errors • Corrections for polarization angle errors and cross-pol contamination • More sophisticated techniques (TBD) to reduce striping Figure 2. a)NEDT compared to requirements and AMSU-A / MHS and b) Radiometric Accuracy, with & without quadratic corrections • Scan-dependent Radiometric Bias • Primarily due to scanning reflector polarized emissivity • Minor secondary effect, may be due to reflector spillover (TBD) • Causes both a systematic angle-dependent error and an overall bias (due to radiometric offset of cold-calibration measurement) b) a) • Conclusions • Stability of critical temperature-dependent parameters is significantly better than predicted • Sensitivity (NEDT) is consistent with ground tests, and is an improvement over AMSU when averaged for equivalent footprint sizes • Other phenomena, such as scan-dependent biases and striping, are being characterized and modeled • Basis for deriving related requirements for future units • Algorithm enhancements are under development to mitigate their effects c) • e: Emissivity = 0.37% • Tref: Reflector Temperature = 0.0° C • y: Scan Angle Figure 3. Channel 1 and channel 17 scan-dependent radiometric biases, observed during pitch-maneuver Figure 1. a) ATMS Channelization Compared to AMSU, b) ATMS Proto-flight Model, and c)Ch 18 TB of Hurricane Isaac Acknowledgments: This work was performed under contract NAS5-01089, sponsored by NASA