CrIMSS EDR Performance Assessment and Tuning

Alex Foo, Xialin Ma and Degui Gu

Sept 11, 2012

Overview

• Updates to CrIS sensor noise LUT and CrIS RTM noise LUT– These LUTs control the inversion of radiances into geophysical state

parameters– Sensor noises can be estimated from operational data– RTM noises can be estimated from analysis of CrIMSS retrieval radiance

residuals

• Coding errors fixes and improvements– Handling of RTM error and sensor error

• Tuning QC thresholds

• Assessed impact on CrIMSS EDR performance

CrIS Sensor Error LUT Evaluation

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CrIS sensor error estimated from uniform scenes

Updating the CrIS sensor error LUT will improve cloud detection performance, but need to be careful not to force the algorithm to fit the noise.

Current Ops LUT

Post-launch Estimate (preliminary)

Channels used in cloud detection

CrIS RTM Error LUT Evaluation

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CrIS RTM error estimated from radiance residuals

“RTM error” is designated to account for the non-sensor cause of radiance mismatch between the observed and the calculated. This LUT can be tuned to improve both EDR quality and yield.

Current Ops LUT

Post-launch Estimate (preliminary)

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Comparison of MW and MW+IR Retrieval Convergence Rates

Scene Condition NGAS (Xu Clim. LUTs) NGAS (Xu Clim. LUTs, NGAS error LUTs)

MW ChiSq Pass Rate

IR ChiSq Pass Rate

MW+ IR ChiSq Pass Rate (Stage 2)

MW ChiSq Pass Rate

IR ChiSq Pass Rate

MW+ IR ChiSq Pass Rate (Stage 2)

All Profiles 84.66% 80.92% 28.87% 84.55% 81.51% 27.92 %

Day Profiles 87.48% 78.41% 28.05% 87.45% 80.00% 27.13%

Night Profiles 83.60% 83.32% 29.65% 83.76% 82.96% 28.68%

Clear Profiles 81.44% 73.92% 15.22% 82.13% 78.20% 16.56%

Partly Cloudy Profiles

85.44% 81.44% 36.77% 86.41% 83.70% 32.75 %

Cloudy Profiles 87.12% 88.99% 28.74% 21.28% N/A N/A

Profiles with Precip. 49.64% 50.86% 12.44% 49.50% 51.04% 12.05%

Profiles w/o Precip. 85.19% 81.38% 29.12% 85.08% 81.97% 28.16%

Profiles Over Ocean 88.18% 80.69% 26.68% 88.09% 81.88% 25.75%

Profile Over Land 80.00% 81.72% 33.50% 79.79% 80.87% 32.50%

Profiles Over Coast 73.98% 79.86% 29.32% 73.95% 80.92% 28.46%

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Tuning Quality Control

• Second-stage (IR and MW combined) retrievals are quality controlled based on chi-square values which are essentially the averaged radiance residuals normalized by the combined sensor and RTM noise errors

• Current chi-Square thresholds are set to 1 for IR and 2 for MW

• If a retrieval doesn’t pass the chi-square test, the second-stage retrieval is tossed out and the first stage (MW only) retrieval is reported

• Examination of EDR quality vs. chi-square values indicated that the current thresholds are set too tight and, as a result, many good IR+MW retrievals are thrown away

• The trade study was performed based on the accuracy of the retrieved Tskin. As the threshold value increases, accuracy of the MW+IR combined retrievals decreases and eventually becomes lower than the MW only. The crossover point is the threshold when the IR retrievals are no longer good and should be replaced with MW

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Tskin Retrieval Accuracy and Convergence vs. Chi-Square Thresholds

Cloud Free Ocean Night

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Biases in Retrieved Surface Skin Temperature Could Indicate Needs for Further MW Tuning

• In the study it is also noticed, as shown in the plots on the previous chart, persistent negative biases in the MW-only retrieved surface skin temperatures

• No biases for IR retrieved surface skin temperatures for cloud free retrievals when MW has little impact

• Negative biases are observed for cloudy IR retrievals when MW is used in cloud clearing and MW has more weight on the retrievals

• Further investigation and tuning if necessary to remove residual biases in MW data

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CrIS Sensor and RTM Error LUT Update Impact on EDR Performance

• Second stage MW chi-square threshold set to 5 for the “best” balance between yield and quality

• Limited to warm ocean retrievals and temperature profile EDRs only

• Observed significant improvement over the MX6.3 baseline performance in both yield and quality

– In average, yield improved from 27-30% (MX6.3) to 46-47% (proposed for MX7)

– Accuracy (standard deviation) improved ~0.2K in lower troposphere

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Improved EDR Yield and Quality with LUT Updates and QC Tuning

Night Ocean Scenes Daytime Ocean Scenes

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CrIMSS Provided Superior Sounding Capability

AVTP Quality for Daytime Cloud Free Ocean Scenes

Lower yield due to cloud leakage and MW tuning?

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Next Step

• Fine-tuning ATMS SDR bias correction (surface and moisture channels)

• Evaluating ATMS sensor error LUT

• Evaluating ATMS RTM error LUT

• Evaluating ATMS remap noise reduction LUT

• Refine EDR quality control logic

• Supporting MX7 update delivery