HIMAWARI-8 COHERENT NOISE REDUCTION

Transcription

1 Place image here (10 x 3.5 ) HIMAWARI-8 COHERENT NOISE REDUCTION DR. PAUL GRIFFITH Harris Space and Intelligence Systems, Fort Wayne, Indiana USA NON-EXPORT CONTROLLED THESE ITEM(S) / DATA HAVE BEEN REVIEWED IN ACCORDANCE WITH THE INTERNATIONAL TRAFFIC IN ARMS REGULATIONS (ITAR), 22 CFR PART , AND THE EXPORT ADMINISTRATION REGULATIONS (EAR), 15 CFR 734(3)(b)(3), AND MAY BE RELEASED WITHOUT EXPORT RESTRICTIONS. HARRIS.COM #HARRISCORP AOMSUC-7/AMS-Asia-2/KIMSC-2 S4-7 AHI-8 Coherent Nosie Reduction 25Oct2016

2 AHI-8 First Operational ABI-class Imager; Paradigm Shift in Geostationary Weather Imaging Better spectral, spatial, and temporal resolution improves quality and number of critical data products Improved calibration targets yields more accurate images Interleaved scene collection provides operational flexibility Himawari-8: Full Disk, Japan, and rapid scan interleaved Himawari-8 launched 7 October 2014; Operational 7 July 2015 Himawari-9 launch scheduled for 1 November 2016 Typhoon Dolphin, 16May2015 AHI-8 lunar image courtesy of JMA Data from JMA, Video courtesy of UW/SSEC, CIMSS AOMSUC-7/AMS-Asia-2/KIMSC-2 S4-7 AHI-8 Coherent Nosie Reduction 25Oct2016 2

3 Coherent Noise Observed in Band 7 (3.9 µm) During AHI-8 Instrument-level Testing Band 7 (3.9 µm) SNR lower than expected Signal levels were in family Unexpected coherent noise observed (not present in ABI) Root cause: beat frequency between detector sample rate and power supply frequency Observable in most bands during space looks (zero input radiance, all 14-bits downlinked) Most significant in Band 7 Full characterization performed Temperature, sample rate, integration time, etc. Stable pattern (more than 30 minutes) Mitigation: ground processing algorithm developed by Harris to remove the coherent noise Restores full SNR performance Significant SNR margin against spec for all channels Coherent Noise After Mitigation AOMSUC-7/AMS-Asia-2/KIMSC-2 S4-7 AHI-8 Coherent Nosie Reduction 25Oct2016 3

4 Root Cause: Detector Sample Rate Change Scan rate for AHI-8 and AHI-9 is 14% slower than ABI AHI scan rate = rad/s ABI scan rate = rad/s (AMI is the same) Slower scan rate sufficient to meet JMA s coverage requirements No 5 minute Full Disk requirement Slower scan rate improves SNR Longer sample interval for same angular sample distance Permits longer integration times, improving SNR Also results in lower data rate Easier downlink and less computational burden on ground system Operational difference: detector sample clock no longer synchronized with power supply clock Both derived from same master crystal oscillator Beat frequency between detector sample clock and power supply clock resulted in low-level coherent noise in detector sample data AOMSUC-7/AMS-Asia-2/KIMSC-2 S4-7 AHI-8 Coherent Nosie Reduction 25Oct2016 4

5 Example: Raw Space Look Data Has Standard Deviation of 5.1 AOMSUC-7/AMS-Asia-2/KIMSC-2 S4-7 AHI-8 Coherent Nosie Reduction 25Oct2016 5

6 Power Supply Interference Calibration (PSIC) Algorithm Reduces Standard Deviation by 70% Average RMS residual noise (counts) 390 S1 MH SNR Timeline SLT #1 Standard Deviation = 1.5 counts Time (minutes) Power Supply interference calibration stable over 10 minutes (one timeline iteration) AOMSUC-7/AMS-Asia-2/KIMSC-2 S4-7 AHI-8 Coherent Nosie Reduction 25Oct2016 6

7 Power Supply Interference Calibration Algorithm Improves Image Quality σ = 4.5 Before PSIC σ = 1.5 After PSIC 332 rows x 1028 samples AOMSUC-7/AMS-Asia-2/KIMSC-2 S4-7 AHI-8 Coherent Nosie Reduction 25Oct2016 7

8 PSIC Algorithm Optimized for Operations Algorithm: Time-based Fourier series (sines and cosines) Derived from initial space look Timelines updated to provide 1000-sample space look at start of every timeline to ensure required data is available 667 space look samples used to calculate equation coefficients PSIC coefficients derived once for each detector element and used for entire duration of current timeline iteration (10 minutes) No impact to image latency Computed during slew from space look to blackbody Subtracted from every Earth and calibration scene detector sample as part of calibration process (pipelined) After decompression and before radiometric calibration No swath or image-based processing, hence no significant impact to image latency AOMSUC-7/AMS-Asia-2/KIMSC-2 S4-7 AHI-8 Coherent Nosie Reduction 25Oct2016 8

9 Trade Study Assessed PSIC Accuracy Versus Number of Space Look Samples Used Multiples of 29 samples yield best results Baseline = 667 samples (23*29) AOMSUC-7/AMS-Asia-2/KIMSC-2 S4-7 AHI-8 Coherent Nosie Reduction 25Oct2016 9

10 PSIC Accuracy Characterized As A Function of Number of Fourier Components Used RMS Residual Noise RMS Residual Noise vs. Components Baseline = 24 components Number of Fourier Series Components AOMSUC-7/AMS-Asia-2/KIMSC-2 S4-7 AHI-8 Coherent Nosie Reduction 25Oct

11 PSIC Algorithm Based on Sample Intervals (More Robust Than Time-based Approach), =,, 1 +,, 1 + = = 2 29, =,, λ, = detector element band and row = number of detector sample intervals between start of first space look and start of current swath (equivalent to elapsed time) = power supply interference phase at start of swath = sample within the swath; k = 1 to number of samples in the swath = number of 29-sample cycles used from the space look = 23 = index value of i th most significant frequency of Fourier series (a,b) = cosine and sine coefficients of Fourier series = detector sample value in counts = power supply interference value in counts = detector sample value in counts after PSIC AOMSUC-7/AMS-Asia-2/KIMSC-2 S4-7 AHI-8 Coherent Nosie Reduction 25Oct

12 JMA Has Implemented PSIC For Most Bands Band 7: applied on 18 June 2015 Before start of Himawari-8 operation 02:00 UTC on 7 July 2015 Improves SNR and image quality for all regions of image Bands 1, 2, 4, 5, 6, 10, 11, 12, 13, 14 and 15: applied 05:00 UTC on 9 March 2016 Improves dark regions of images In bright regions shot noise makes coherent noise insignificant PSIC example provided by JMA (Band 4, 0.86 µm, 00:20 UTC on 25 November 2015) Standard intensity scale No PSIC Enhanced intensity scale No PSIC Enhanced intensity scale After PSIC applied AOMSUC-7/AMS-Asia-2/KIMSC-2 S4-7 AHI-8 Coherent Nosie Reduction 25Oct

13 Summary Coherent noise observed in AHI-8 (and AHI-9) instrument level testing Root cause determined: beat frequency between detector sample clock and power supply clock Algorithm to remove the coherent noise (PSIC) developed by Harris, implemented by MELCO, and deployed by JMA Hence, no net impact to Himawari-8 (or 9) operational imagery AOMSUC-7/AMS-Asia-2/KIMSC-2 S4-7 AHI-8 Coherent Nosie Reduction 25Oct