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GOES-R AWG Hydrology Algorithm Team: Rainfall Potential

June 14, 2011

Presented By: Bob KuligowskiNOAA/NESDIS/STAR

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Outline

Executive Summary Algorithm Description ADEB and IV&V Response Summary Requirements Specification Evolution Validation Strategy Validation Results Summary

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Executive Summary

This Rainfall Potential Algorithm generates the Option 2 product of predicted rainfall accumulation for the next 3 h on the ABI grid.

The NOAA / NSSL K-Means algorithm has been adapted to produce extrapolation-based forecasts of rainfall from the current and previous GOES-R Rainfall Rate fields.

Version 3 (80%) was delivered in September 2010. Version 5 (100%) delivery has been delayed 12 months in response to GPO guidance.

Preliminary validation of the version 3 algorithm has been performed against 20 days of SEVIRI data from 2005.

Validation against Nimrod radar indicates spec compliance.

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Algorithm Description

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Algorithm Description

This Rainfall Potential Algorithm generates the Option 2 product of predicted rainfall accumulation for the next 3 h on the ABI grid using the NOAA / NSSL K-Means algorithm.

Rainfall is extrapolated based on a comparison of current and previous Rainfall Rate imagery» ONLY motion is extrapolated (no growth / decay)

» No initiation in an extrapolation-based approach

Three basic algorithm components:» Identify features in rain rate imagery

» Determine motion between features in consecutive images between features in consecutive images

» Apply motion vectors to create rainfall nowcastsApply motion vectors to create rainfall nowcasts

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Motivation for Algorithm Selection

In 2007 the Hydrology AT compared the results from 4 different experimental real-time rainfall forecasting algorithms:» Hydro-Nowcaster (NESDIS / STAR)

» K-Means (NOAA / NSSL)

» TITAN (UCAR)

» MAPLE (McGill University)

MAPLE gave the best results but licensing issues could not be resolved; K-Means (second-base performer) was selected instead.

Example Rainfall Potential Output

Rainfall Potential from 1500-1800 UTC 8 July 2005 derived from Rainfall Rate fields (retrieved from SEVIRI data) at 1445 and 1500 UTC.

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ADEB and IV&V Response Summary

ADEB did not recommend advancing to 100%, stating “the algorithm needs more validation and reconsideration of the choice of algorithm.”

As a result, the algorithm development schedule has been delayed by 12 months.

Regarding “reconsideration of the choice of algorithm”, the AT responded that the algorithm selection process was well-documented and that validation has been made difficult by the paucity of validation data. The AT also requested clarification on these comments.

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ADEB and IV&V Response Summary

Regarding “the algorithm needs more validation”, high-quality rainfall data at time scales of 3 h or less have been extremely difficult to find. Planned solutions:» CHUVA (Brazil) field campaign data» Global Precipitation Climatology Center (GPCC) gauge data

(can only be used in-house—visit in summer 2012?)» EUMETSAT Hydrology SAF—reaching out to see if their data

(also in-house only) could be used via a visit.

In response to a phone request, the AT also surveyed users from OSPO/SAB, NWS/HPC, NWS/OHD, and NWS/WGRFC and found significant interest in the product and for it to be available at launch.

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Requirements Specification Evolution

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Temporal Coverage Qualifiers

Product Extent QualifierCloud Cover Conditions Qualifier

Product Statistics Qualifier

Day and night Quantitative out to at least 70 degrees LZA or 60 degrees latitude, whichever is less, and qualitative beyond

N/A Over rainfall cases

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Validation Strategy

Validation Strategy

Since the requirement is for rainfall accumulations of 3 h, radar and short-term gauges are the only available source of data for validation against spec

Ground-based radars:» Nimrod radars in UK and

Western Europe—5-km grid composite

Sample Nimrod 3-h accumulation

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Validation Strategy

Derive rainfall potential from rainfall rates retrieved from GOES-R ABI proxy data

» Meteosat-8 SEVIRI inputs to rainfall rates: Bands 5 (6.2 µm), 6 (7.3 µm), 7 (8.7 µmµm), 9 (10.8 µm), and 10 (12.0 µm)

Collocate (in space and time) derived rainfall potential with ground validation rainfall accumulations

» 3-hour observed rainfall accumulation derived from Nimrod radar

Generate comparative statistics (satellite rainfall accumulation – ground truth rainfall accumulation)

» Accuracy

» Precision

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Validation Results

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Rainfall Potential Validation

CDF’s of (absolute) errors of Rainfall Potential vs.CDF’s of (absolute) errors of Rainfall Potential vs. Nimrod radar data (Western Nimrod radar data (Western Europe only) for the 5Europe only) for the 5thth-9-9thth of April, July, and October 2005. of April, July, and October 2005.

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Rainfall Potential Validation vs. Spec

Validation versus Nimrod radar data (covering Western Europe only) for Validation versus Nimrod radar data (covering Western Europe only) for 15 days of data: 6-915 days of data: 6-9thth of April, July, and October 2005: of April, July, and October 2005:

F&PS Evaluation vs. Nimrod radar

mm Accuracy Precision Accuracy Precision

Rainfall Potential 5.0 5.0 2.4 3.1

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Next Steps AIT determined that the highly object-oriented C++ K-

Means code could not be readily implemented into the prototype framework

Consequently, NSSL has been asked to deliver a detailed ATBD and the algorithm is being re-coded from it

Once this is done, the K-Means parameters will be tuned to further enhance algorithm performance:

» Experiment with growth / decay option (currently turned off)

» Alter minimum rainfall threshold to reduce effects of light rain on motion estimates

» Tune scaling parameters

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Summary

This Rainfall Potential Algorithm generates the Option 2 product of predicted rainfall accumulation for the next 3 h on the ABI grid.

The NOAA / NSSL K-Means algorithm has been adapted to produce extrapolation-based forecasts of rainfall from the current and previous GOES-R Rainfall Rate fields.

Version 3 (80%) was delivered in September 2010. Version 5 (100%) delivery has been delayed 12 months in response to GPO guidance.

Preliminary validation of the version 3 algorithm has been performed against 20 days of SEVIRI data from 2005.

Validation against Nimrod radar indicates spec compliance.