Brad Fisher

Ground Validation for the Tropical Rainfall Measuring Mission (TRMM)

Abstract An overview of the Tropical Rainfall Measuring Mission (TRMM) Ground Validation (GV) Program is presented. This ground validation (GV) program is based at NASA Goddard Space Flight Center in Greenbelt, Maryland, and is responsible for processing several TRMM science products for validating space-based rain estimates from the TRMM satellite. These products include gauge rain rates, and radar-estimated rain intensities, type, and accumulations, from four primary validation sites (Kwajalein Atoll, Republic of the Marshall Islands; Melbourne, Florida; Houston, Texas; and Darwin, Australia). Site descriptions of rain gauge networks and operational weather radar configurations are presented together with the unique processing methodologies employed within the Ground Validation System (GVS) software packages. Rainfall intensity estimates are derived using the Window Probability Matching Method (WPMM) and then integrated over specified time scales. Error statistics from both dependent and independent val...

Comparisons of Instantaneous TRMM Ground Validation and Satellite Rain Rate Estimates at Different Spatial Scales

Abstract This study provides a comprehensive intercomparison of instantaneous rain rates observed by the two rain sensors aboard the Tropical Rainfall Measuring Mission (TRMM) satellite with ground data from two regional sites established for long-term ground validation: Kwajalein Atoll and Melbourne, Florida. The satellite rain algorithms utilize remote observations of precipitation collected by the TRMM Microwave Imager (TMI) and the Precipitation Radar (PR) aboard the TRMM satellite. Three standard level II rain products are generated from operational applications of the TMI, PR, and combined (COM) rain algorithms using rain information collected from the TMI and the PR along the orbital track of the TRMM satellite. In the first part of the study, 0.5° × 0.5° instantaneous rain rates obtained from the TRMM 3G68 product were analyzed and compared to instantaneous Ground Validation (GV) program rain rates gridded at a scale of 0.5° × 0.5°. In the second part of the study, TMI, PR, COM, and GV rain rates ...

Estimating Rain Rates from Tipping-Bucket Rain Gauge Measurements

Abstract This paper describes the cubic spline–based operational system for the generation of the Tropical Rainfall Measuring Mission (TRMM) 1-min rain-rate product 2A-56 from tipping-bucket (TB) gauge measurements. A simulated TB gauge from a Joss–Waldvogel disdrometer is employed to evaluate the errors of the TB rain-rate estimation. These errors are very sensitive to the time scale of rain rates. One-minute rain rates suffer substantial errors, especially at low rain rates. When 1-min rain rates are averaged over 4–7-min intervals or longer, the errors dramatically reduce. Estimated lower rain rates are sensitive to the event definition whereas the higher rates are not. The median relative absolute errors are about 22% and 32% for 1-min rain rates higher and lower than 3 mm h−1, respectively. These errors decrease to 5% and 14% when rain rates are used at the 7-min scale. The radar reflectivity–rain-rate distributions drawn from the large amount of 7-min rain rates and radar reflectivity data are mostl...

Assessing the Relative Performance of Microwave-Based Satellite Rain-Rate Retrievals Using TRMM Ground Validation Data

Abstract Spaceborne microwave sensors provide critical rain information used in several global multisatellite rain products, which in turn are used for a variety of important studies, including landslide forecasting, flash flood warning, data assimilation, climate studies, and validation of model forecasts of precipitation. This study employs 4 yr (2003–06) of satellite data to assess the relative performance and skill of the Special Sensor Microwave Imager [SSM/I (F13, F14, and F15], Advanced Microwave Sounding Unit [AMSU-B (N15, N16, and N17)], Advanced Microwave Scanning Radiometer for Earth Observing System [AMSR-E (Aqua)], and the Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI) in estimating surface rainfall based on direct instantaneous comparisons with ground-based rain estimates from the TRMM Ground Validation (GV) sites at Kwajalein, Republic of the Marshall Islands (KWAJ), and Melbourne, Florida (MELB). The relative performance of each of these satellite estimates is examined v...

Climatological Processing and Product Development for the TRMM Ground Validation Program

Abstract A comprehensive Ground Validation (GV) Program has been implemented to validate TRMM satellite observations. The primary goal of TRMM GV is to provide basic validation of satellite-derived precipitation measurements over monthly climatologies for the following primary sites: Melbourne Florida (FL); Houston Texas (TX); Darwin, Australia; and Kwajalein Atoll Republic of Marshall Islands (RMI). As part of the TRMM GV effort, research analysts at NASA Goddard Space Flight Center (GSFC) generate standardized rainfall products using quality-controlled ground-based radar data from the four primary GV sites. An overview of TRMM GV climatological processing and product generation, including description of the data flow between primary GV sites, NASA GSFC, and the TRMM Science Data and Information System (TSDIS) is presented. The radar data quality control (QC) algorithm, which features eight adjustable height and reflectivity parameters, together with the methodology used to create standardized monthly, gauge-adjusted rainfall products for each primary site is summarized. Presented are statistics from recently reprocessed official GV radar rainfall products which include derived monthly gauge bulk-adjusted Z-R relationships area-averaged rain rates, radar-to-gauge accumulation ratios, gauge acceptance/rejection ratios and radar data availability. Climatological GV products, statistics, and descriptions can be found at the Internet address http://trmm gsfc.nasa.gov/TRMMGV/GVproducts.html .

Evaluation of Radar Rainfall Products: Lessons Learned from the NASA TRMM Validation Program in Florida

Abstract Evaluation of the Tropical Rainfall Measuring Mission (TRMM) satellite observations is conducted through a comprehensive ground validation (GV) program. Since the launch of TRMM in late 1997, standardized instantaneous and monthly rainfall products are routinely generated using quality-controlled ground-based radar data adjusted to the gauge accumulations from four primary sites. As part of the NASA TRMM GV program, effort is being made to evaluate these GV products. This paper describes the product evaluation effort for the Melbourne, Florida, site. This effort allows us to evaluate the radar rainfall estimates, to improve the algorithms in order to develop better GV products for comparison with the satellite products, and to recognize the major limiting factors in evaluating the estimates that reflect current limitations in radar rainfall estimation. Lessons learned and suggested improvements from this 8-yr mission are summarized in the context of improving planning for future precipitation mis...

Satellite Sampling and Retrieval Errors in Regional Monthly Rain Estimates from TMI, AMSR-E, SSM/I, AMSU-B, and the TRMM PR

AbstractPassive and active microwave rain sensors on board Earth-orbiting satellites estimate monthly rainfall from the instantaneous rain statistics collected during satellite overpasses. It is well known that climate-scale rain estimates from meteorological satellites incur sampling errors resulting from the process of discrete temporal sampling and statistical averaging. Sampling and retrieval errors ultimately become entangled in the estimation of the mean monthly rain rate. The sampling component of the error budget effectively introduces statistical noise into climate-scale rain estimates that obscures the error component associated with the instantaneous rain retrieval. Estimating the accuracy of the retrievals on monthly scales therefore necessitates a decomposition of the total error budget into sampling and retrieval error quantities. This paper presents results from a statistical evaluation of the sampling and retrieval errors for five different spaceborne rain sensors on board nine orbiting sa...

Evolving improvements to TRMM ground validation rainfall estimates

Abstract The primary function of the TRMM Ground Validation (GV) Program is to create GV rainfall products that provide basic validation of satellite-derived precipitation measurements for select primary sites. Since the successful 1997 launch of the TRMM satellite, GV rainfall estimates have demonstrated systematic improvements directly related to improved radar and rain gauge data, modified science techniques, and software revisions. Improved rainfall estimates have resulted in higher quality GV rainfall products and subsequently, much improved evaluation products for the satellite-based precipitation estimates from TRMM. Early improvements in TRMM GV rainfall products involve replacing a default radar reflectivity (Z e ) — rain rate (R) relationship with convective and stratiform relationships independently derived using bulk-adjusted, quality-controlled rain gauge data. Upon the development of an automated gauge quality control procedure, poorly correlated gauge-radar data in the bulk-adjustment process are ignored and Z e -R relationships are again refined. These Z e R relationships, applied to base scan reflectivity data to produce GV rain maps, are further modified as improvements to intermediate radar and gauge products result in more realistic and internally consistent rainfall statistics. Additionally, improvements to radar and gauge data from the primary GV sites further increase the reliability of rainfall products. Rainfall accumulation statistics for each primary site are presented, demonstrating the evolving improvement in radar rainfall estimation for each successive generation of products. Current generations of GV rainfall products, based on more robust data and science techniques, have removed known biases in radar rainfall estimates. Increased confidence in GV rainfall products results in more meaningful comparisons with satellite-derived precipitation estimates from TRMM.

An overview of the Keys area precipitation project (KAPP)

As part of the NASA tropical rainfall measuring mission ground validation (TRMM-GV) program, a field campaign was conducted in Florida Keys during August-September 2002. The purpose of the field campaign was to study the characteristics of rainfall over the Florida Keys, utilizing Key West WSR-88D, NASAs s-band polarimetric radar (NPOL), and a network of rain gauges and disdrometers. This study focuses on the performance of the rain gauges and disdrometers and its impact on the radar rainfall algorithms.