An Overview of Satellite Rainfall Estimation for Flash Flood Monitoring Timothy Love NOAA Climate Prediction Center with USAID- FEWS-NET, MFEWS, AFN Presented at the International Workshop on Flash Flood Forecasting March San Jose, Costa Rica

Why Use Satellite-Based Techniques? Failure to Capture Significant Rainfall

Why Use Satellite-Based Techniques?

Geostationary Infrared Satellite Technology GOES °WGOES °W

Geostationary Infrared Satellite Technology Detects upwelling of Infrared radiation from nearest surface This radiation is converted to a Temperature; Colder temperatures are generally associated with a higher altitude An approximation can be made that a cloud higher in the atmosphere produces more precipitation than a ‘lower’ cloud  Cloud Top Temperature vs Rain rate Therefore, generally:

Negative IR Rainfall Aspects  Rainfall estimation method is not physical  Errors sensing high level, non precipitating clouds such as cirrus  Failures to capture some warm cloud processes such as coastal rainfall and processes such as coastal rainfall and orographics orographics

Positive Aspects of GOES IR Temporal and spatial resolution! Temporal and spatial resolution! ¼ to ½ hour frequency & 2-4 Km pixel resolution¼ to ½ hour frequency & 2-4 Km pixel resolution Geostationary imaging Geostationary imaging Rapid data availability Rapid data availability Easily accessible Easily accessible

Microwave Satellite Sources AMSU-B SSM/I TMI

Microwave Satellite Technology Passive MW rainfall retrieval methods are more physical then IR sensors Passive MW rainfall retrieval methods are more physical then IR sensors MW instrument measures scattered radiation from ice & water particles over land MW instrument measures scattered radiation from ice & water particles over land Sensors measure ice & water particle distribution Sensors measure ice & water particle distribution The contribution due to ice is correlated to The contribution due to ice is correlated to previously determined radar – rain rate previously determined radar – rain rate relationships relationships

Negative MW Rainfall Aspects CCCCoarse spatial and temporal resolution 11116-25 Km pixel & ~2 hour sampling HHHHIGH LATENCY TTTThough predictable, satellite tracks are not consistent between observations PPPProblematic when attempting to sense H2O over snow/ice covered regions

Positive Aspects of MW Method MW rain rate estimation is a physical method MW rain rate estimation is a physical method Convective systems yield higher accurate rain rate estimates Convective systems yield higher accurate rain rate estimates

TRMM Sensors VIRS (Visible and InfRared Scanner) VIRS (Visible and InfRared Scanner) –Swath width: 720 km –Resolution: 2.1+ km TMI (TRMM Microwave Imager) TMI (TRMM Microwave Imager) –Swath width: 760 km –Resolution: 5-45 km

TRMM Sensors, Cont. PR (Precipitation Radar) PR (Precipitation Radar) –Swath width: 220 km –Resolution: 4.3 km

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