Precipitation is a critical component of the Earth's hydrological cycle. Launched on 27 November 1997, TRMM is a joint U.S.–Japan satellite mission to provide the first detailed and comprehensive dataset of the four-dimensional distribution of rainfall and latent heating over vastly undersampled tropical and subtropical oceans and continents (40°S–40°N). Over the past 14 years, TRMM has been a major data source for meteorological, hydrological, and other research and application activities around the world.
This short article describes how the NASA Goddard Earth Sciences Data and Information Services Center (GES DISC) provides TRMM archive and nearreal- time precipitation datasets and services for research and applications. TRMM data consist of orbital data from TRMM instruments at the sensor's resolution, gridded data at a range of spatial and temporal resolutions, subsets, ground-based instrument data, and ancillary data. Data analysis, display, and delivery are facilitated by the following services: (1) Mirador (data search and access); (2) TOVAS (TRMM Online Visualization and Analysis System); (3) OPeNDAP (Opensource Project for a Network Data Access Protocol); (4) GrADS Data Server (GDS); and (5) Open Geospatial Consortium (OGC) Web Map Service (WMS) for the GIS community. Precipitation data application services are available to support a wide variety of applications around the world. Future plans include enhanced and new services to address data-related issues from the user community. Meanwhile, the GES DISC is preparing for the Global Precipitation Measurement (GPM) mission, which is scheduled for launch in 2014.
Precipitation is a critical component of Earth's hydrological cycle. Launched on 27 November 1997, the NASA Tropical Rainfall Measuring Mission (TRMM) is a joint U.S.–Japan satellite mission to provide the first detailed and comprehensive dataset of the four-dimensional distribution of rainfall and latent heating over vastly undersampled tropical and subtropical oceans and continents (40°S–40°N). Over the past 14 years, TRMM has been a major data source for meteorological, hydrological, and other research and application activities around the world. For example, major achievements in fundamental new information on the synoptic climatology of tropical rainfall and weather systems are summarized in the 2006 National Research Council assessment report:
detailed vertical profiles of precipitation and latent heating;
quantitative determination of the relative contributions of stratiform and convective precipitation;
description of the finescale structure of rainfall systems that can be determined from the PrecipitationRadar (PR) data; and
documentation of lightning and convection relationships over land and ocean.
There are five instruments onboard the TRMM satellite, and four of them are used for precipitation (Table 1). Standard TRMM products from the Visible and Infrared Scanner (VIRS), the TRMM Microwave Imager (TMI), and PR are archived at and distributed from the NASA Goddard Space Flight Center (GSFC) Earth Sciences Data and Information Services Center (GES DISC). The Lightning Imaging Sensor (LIS) data products are archived at the NASA Global Hydrology Resource Center (GHRC). In addition to these four instruments, data products from the Clouds and Earth's Radiant Energy System (CERES) are archived at the Atmospheric Science Data Center (ASDC) at the NASA Langley Research Center.
In August 2001, the TRMM satellite was boosted from 350 to 402.5 km to extend its lifespan by reducing the consumption rate of the fuel used to maintain its orbit altitude. As of this writing, TRMM is still in operation and has continually collected data. Since 1997, more than 14 years of TRMM data have been collected. This article is to inform that the GES DISC provides free, quasiglobal archive and near-real-time precipitation products and services for research and applications.
TRMM PRODUCT OVERVIEW.
TRMM data products archived at and distributed from the GES DISC are organized as the following three categories: 1) orbital products (also known as swath products); 2) gridded products; and 3) other TRMM-related products, consisting of TRMM ancillary products, ground-based instrument products, TRMM and ground observation subsets, and field experiment products. Table 2 lists raw and calibrated satellite-swath data, as well as geophysical swath products derived from VIRS, TMI, PR, and combined TMI/PR, such as 2A12 TMI hydrometeor profiles, 2A23 radar rain characteristics, and 2B31 combined rainfall profiles, etc. LIS science data contain orbital lightning products distributed by GHRC. Table 3 lists products that have been gridded and averaged spatially (0.25° × 0.25° to 5° × 5°) and temporally (hours to 1 month). For example, 3A25 provides global rain rate from PR alone. The collection of these monthly products allows intercomparison to understand precipitation biases and uncertainty. Two multisatellite precipitation products, the 3-hourly and monthly TRMM Multi-Satellite Precipitation Analysis (TMPA) products (3B42, 3B43), are the most popular because of their high spatial and temporal resolutions. The daily product derived from 3B42 is also popular for those who do not want high temporal resolution products.
Table 4 lists other TRMM-related products. The NOAA National Centers for Environmental Prediction (NCEP)/Climate Prediction Center (CPC) globally merged (60°N–60°S), half-hourly, 4-km infrared brightness temperature data (equivalent blackbody temperatures, merged from several geostationary satellites around the globe) are an ancillary product not only for precipitation algorithm development, but also for providing background information for TRMM and other meteorological event case studies. Data from ground-based instruments provide radar data products from 10 TRMM project-affiliated ground stations in the tropical and subtropical regions. Table 4 also describes subsets from 1) ground validation Coincidence Subsetted Intermediate data (CSI), consisting of a single volume scan (VOS) when the satellite nadir is within a specified distance from a ground validation site, or a gridded field associated with a VOS, which is coincident with a satellite overpass; 2) gridded subsets of orbital data products derived from VIRS, TMI and PR; and 3) collection of TRMM satellite instrument scan data when the satellite nadir is within a specified distance from a ground validation or experiment site. These value-added subsets facilitate TRMM ground validation and other research activities, because users do not need to download the entire original orbital data and perform the subsetting task themselves.
The TRMM field campaign program was designed to provide independent ground truth for use in algorithm development for TRMM satellite measurements. TRMM field campaigns employ ground-based radars, rain gauge networks, and aircraft measurements from the NASA DC-8 and ER2, with instrumentation similar to TMI and PR. TRMM field campaigns consist of Texas-Florida Underflight (TEFLUN A and TEFLUN B); Large-scale Biosphere- Atmosphere Experiment in Amazonia (TRMM-LBA); Kwajalein Experiment (KWAJEX); South China Sea Monsoon Experiment (SCSMEX); Convection And Moisture EXperiment (CAMEX); and Tropical Ocean Global Atmospheres/Coupled Ocean Atmosphere Response Experiment (TOGA-COARE).
TRMM PRECIPITATION DATA SERVICES.
Providing TRMM data services is very important for expediting research and applications and maximizing the societal benefits from the TRMM mission. Using remote-sensing products can be a daunting task due to a number of problems, such as data format conversion, large data volume, lack of software, etc. Value-added data services can reduce data processing time and thus increase the time spent on scientific investigations and applications. New users are more likely to evaluate and use TRMM products if user-friendly data services are provided. Since TRMM was launched, several data services (Table 5) have been developed and/or applied at the GES DISC. In particular:
Mirador. Mirador (Fig. 1) is designed to facilitate data searching, accessing, and downloading. Mirador consists of a search and access web interface developed in response to the search habits of data users. It has a drastically simplified, clean interface and employs the Google mini-appliance for metadata keyword searches. Other features include quick response, data file hit estimator, Gazetteer (geographic search by feature name capability), and an interactive shopping cart. Value-added services include several data format conversions and spatial subsetting for a number of popular products.
Giovanni TOVAS. To enable scientific exploration of Earth science data products without going through complicated and often time-consuming data processing steps (i.e., data downloading, data processing), the GES DISC has developed the GES-DISC Interactive Online Visualization and Analysis Infrastructure (Giovanni), based on user support experience and in consultation with members of the user community. The TRMM Online Visualization and Analysis System (TOVAS) is a member of the Giovanni family. Giovanni is characterized by the capabilities for quick data search, subset, analysis, display, and download. With Giovanni, customized analysis, visualization, and data can be obtained from the built-in functions, such as latitude–longitude maps, time series, Hovemöller diagrams, etc. Further analysis using other software can be done with customized data downloaded from Giovanni. In short, Giovanni can allow access to data products without downloading data and software. For example, Fig. 2 is a rainfall map of the near-real-time TRMM Multi-Satellite Precipitation Analysis (TMPA-RT, or 3B42RT) generated from TOVAS, showing the record rains that Typhoon Morakot dumped on southern Taiwan on 8–9 August 2009 on Google Earth. Over the years, TOVAS has proven to be very popular with users for online accessing of TRMM and other precipitation data products. TOVAS will continue to evolve to accommodate the Global Precipitation Mission (GPM) data and the expected increase in multisensor data product intercomparisons.
Other data services. Users of TRMM products can benefit from several other data services listed in Table 5. The TRMM software developed at the GES DISC can read in all TRMM standard products and write out user-selected parameter arrays and other data in flat binary or ASCII files. The Orbit Viewer Tool for High-resolution Observation Review (THOR), developed by the Precipitation Processing System (PPS) at the GSFC, is a convenient stand-alone tool to visualize all TRMM standard products.
Figure 3 is an example of using Orbit Viewer THOR to plot a 3D 10-dBZ isosurface from the first spaceborne precipitation radar, showing an intensifying tropical cyclone, Giovanna, near the east-northeast of Madagascar in the Indian Ocean at 1200 UTC on 11 February 2012. The Simple Subset Wizard (SSW) tool allows spatial subsetting and provides outputs in NetCDF and ASCII. REVERB is a tool that allows keyword, spatial, and temporal searches. The GrADS Data Server (GDS, formerly known as GrADS-DODS Server) is a stable, secure data server that provides subsetting and analysis services across the internet and offers a convenient way for GrADS users to access TRMM data. The core of GDS is the Open Source Project for a Network Data Access Protocol (OPeNDAP, also known as Distributed Oceanographic Data System or DODS), which provides remote access to individual variables within datasets in a form usable by many tools, such as Interactive Data Viewer (IDV), McIDAS-V, Panoply, Ferret, and GrADS. The Open Geospatial Consortium (OGC) Web Map Service (WMS) provides map depictions over the network via a standard protocol and enables clients to build customized maps with data coming from different networks.
TRMM APPLICATION SERVICES.
TRMM mission societal benefits have been realized through the use of data services for precipitation applications, such as flood monitoring, often requiring near-real-time precipitation data services support. In addition to the resources described in Section 3, the GES DISC provides such support through the following services:
Near-real-time precipitation product access through ftp, GDS, and WMS. Customized application software can be developed to directly access data via FTP, GDS, and WMS. For example, monthly total rainfall from 3B43 is provided to the NASA Earth Observations (NEO) via WMS.
Value-added products to expedite TRMM applications, such as two daily products derived from 3B42 and 3B42RT (the near-real-time version of 3B42), respectively, and an accumulated rainfall product from 3B43.
Daily global and regional maps of current conditions for monitoring precipitation and its anomalies around the world. To provide a simple and quick way to monitor global droughts and floods, we routinely generate global and regional maps of rainfall accumulation, rainfall anomaly, and normalized anomaly (anomaly/climatology), ranging from 3-hourly to 90 days. The maps are updated daily.
The GES DISC Hurricane Portal, which provides near-real-time monitoring services and an imagery archive for the Atlantic basin. The Hurricane Data Analysis Tool (HDAT) provides easy access to NASA Quick Scatterometer (QuikSCAT) ocean surface wind data, TMPA precipitation, TMI SST, NCEP Reanalysis, and NCEP/CPC global merged IR dataset.
The U.S. Department of Agriculture's Foreign Agricultural Service (USDA FAS) Crop Explorer. In collaboration with the GES DISC, USDA FAS is routinely using near-real-time global satellite-derived precipitation data (i.e., 3B42RT) to monitor crop conditions around the world. This project is unique, being the first of its kind to utilize satellite precipitation data in an operational manner. Satellite precipitation products are produced by NASA via a semiautomated process and made publicly accessible from the USDA FAS's Crop Explorer website. Monitoring precipitation for agriculturally important areas around the world greatly assists the USDA FAS in quickly locating regional weather events, as well as helping improve crop production estimates. Figure 4 is an example of the TRMM near-real-time product (3B42RT) in USDA Crop Explorer. Figure 4a contains a global map for selecting a region of interest and Fig. 4b is a sample of 10-day accumulated rainfall derived from 3B42RT in southern Africa and its percent normal (normalized anomaly).
In addition to applications at the GES DISC, TRMM data have been used in a wide variety of activities around the globe. Applications reported by TRMM users range from meteorology and hydrology to other areas as well, such as development of a rainfall-based crop insurance product for developing countries, a study on environmental causes of diabetes using rainfall as an effect on crop moisture and toxins, an early warning system for mosquito-borne diseases, etc.
Future plans include new and enhanced data services to address user needs and support applications. Meanwhile, the GES DISC is preparing for the GPM era. Scheduled for launch in 2014, GPM consists of a core observatory that will serve as a reference standard to a constellation of research and operational microwave sensors to provide uniformly calibrated precipitation measurements around the globe every 2–4 hours for research and applications. As of this writing, three types of scientific data products will be generated: near-real-time products, research products, and outreach data products. The near-real-time and outreach products will be created within short time spans to meet the particular needs of their end users. The research products are full data products of research quality. With an increasing number of instruments and improved spatial and temporal resolutions and coverage, it is expected that GPM data volume will greatly exceed that of TRMM. Nonetheless, the GES DISC will continue to provide the existing data services for GPM, and in the meantime, to develop services for improving data accessibility and discovery, as well as addressing new issues arising from the user community.