IDL Helps Scientists Measure Global Rainfall

IDL -- The Choice for Scientists when Ingesting, Analyzing, and Visualizing Radar Data

IDL Helps Scientists Measure Global Rainfall

Background

The Global Precipitation Measurement (GPM) mission, a joint mission between NASA and the Japan Aerospace Exploration Agency (JAXA), is an international network of satellites that will provide the next-generation global observations of rain and snow. The GPM concept centers on the deployment of a “core” satellite carrying an advanced radar/radiometer system to measure precipitation from space and serve as a reference standard to unify precipitation measurements from a constellation of research and operational satellites. The GPM Core Observatory is scheduled for launch in early 2014. The goal is to develop high-resolution, near-real-time global precipitation data products by combining all available information from space and ground-based measurements. Through these improved measurements, the GPM mission will help advance our understanding of Earth’s water and energy cycle, improve forecasting of extreme events that cause natural hazards and disasters, and extend current capabilities in using accurate and timely information of precipitation to directly benefit society.

Customer Challenge

In support of the Tropical Rainfall Measuring Mission’s (TRMM) Global Validation Program, the NASA TRMM Satellite Validation Office created the Radar Software Library (RSL), a C-based library for ingesting, analyzing and outputting several common radar data formats. However, working with C can be cumbersome and time consuming.

Reflectivity image from June 12, 2013. he storms highlighted by the black circles are tornadic, as evidenced by the hook echoes on the SW sides of the echoes.

Solution Achieved

The IDL version of RSL (RSL_IN_IDL), provides a more scientist-friendly interface for ingesting, analyzing and visualizing radar data. This provides the utility of RSL in an IDL environment. The TRMM/GPM Ground Validation team also used IDL to develop ingest routines of numerous common radar data formats such as WSR-88D (Level II), Sigmet, Lassen, Universal Format and others.

Ground Validation Field Experiment

Ground Validation (GV) is an integral element of the mission as GV converts satellite instrument data to useful information about rainfall and snowfall. GV consists of collecting data from ground-based radar rain gauges and disdrometers. The data is quality-controlled, and then validation products are produced for comparison with satellite products.

David Wolff, a research scientist and meteorologist with NASA Wallops Flight Facility is part of a team supporting GV program activities of the GPM mission. He and at least 100 other people from NASA, University of Iowa, Colorado State University and other institutions spent much of the Spring of 2013 conducting a field experiment to support the GPM mission known as the Iowa Flood Studies (IFloodS) field campaign. This campaign was the first hydrological-focused GV campaign for GPM and included measurements by state-of-the-art multi-parameter radars, disdrometers and an extensive network of rain gauges, stream sensors and soil moisture probes.

If You Build It, They will Come

Turns out that putting big fancy equipment in a cornfield attracts some attention from the locals. “We were about five miles from the city of Traer, IA,” said Mr. Wolff. Once the local schools heard what was happening, the big yellow busses started delivering students to the site for field trips. Mr. Wolff estimates that some 100 school kids and teachers from 1st through 12th grade flocked to the site to get a lesson in GV and global precipitation.

A solar array wing begins to release from the GPM Core satellite in a deployment test on Thursday, June 6, 2013. Image courtesy of NASA Goddard Space Flight Center.

Mr. Wolff uses IDL extensively when working with GV radar data. “It’s the only computer language I use, and I use it every day,” says Mr. Wolff. “I was generating near-real-time radar products in the field while I was still working out some issues with the code.” says Mr. Wolff who noted that the NV5 (formerly Exelis VIS) support team helped keep his team up and running while in the field.

“A lot of the radar data [processing routines] are written in C. It’s painful to work in C,” says Mr. Wolff. In support of the Tropical Rainfall Measuring Mission’s (TRMM) Global Validation Program, the NASA TRMM Satellite Validation Office created the Radar Software Library (RSL), a C-based library for ingesting, analyzing and outputting several common radar data formats. Mr. Wolff primarily works with the IDL version of RSL (RSL_IN_IDL), which provides a more scientist-friendly interface for ingesting, analyzing and visualizing radar data. The idea is to provide the utility of RSL in an IDL environment.

As in RSL, the primary data object is the radar structure, which provides a consistent interface for a variety of radar formats. This is the structure returned by rsl_anyformat_to_radar, the generic function for reading a raw radar data file. The IDL version of the radar structure is essentially the same as its C language counterpart, so users of RSL should find it familiar. The most important difference in the IDL version is that data is stored directly in structures, so functions for packing and unpacking data are no longer needed. Once the data are ingested, IDL provides a broad library of analysis routines, in an easy-to-use language, that allows scientists to quickly extract meaningful information from raw data.

The GPM Dual-frequency Precipitation Radar (DPR) integrated on the GPM Core Observatory. Image courtesy of NASA Goddard Space Flight Center.

The GPM mission is building on the success of TRMM’s highly successful rain-sensing packages, which focused primarily on heavy to moderate rain over tropical and subtropical oceans. GPM will extend coverage to higher latitudes to provide a global view of precipitation and will also provide near-real-time information. Since light rain and falling snow account for significant fractions of precipitation occurrences in middle and high latitudes, a key advancement of GPM is the extended capability to measure light rain (< 0.5 mm hr-1), solid precipitation and the microphysical properties of precipitating particles. This capability drives the designs of both the active and passive microwave instruments on GPM. The Core Observatory will then act as a reference standard for the precipitation estimates acquired by the GPM constellation of sensors.

GPM will provide global precipitation measurements with improved accuracy, coverage and dynamic range for studying precipitation characteristics. GPM is expected to improve weather and precipitation forecasts through assimilation of instantaneous precipitation information. Relative to TRMM, the enhanced measurement and sampling capabilities of GPM will offer many advanced science contributions and societal benefits:

• Improved knowledge of the Earth’s water cycle and its link to climate change
• New insights into storm structures and large-scale atmospheric processes
• New insights into precipitation microphysics
• Advanced understanding of climate sensitivity and feedback processes
• Extended capabilities in monitoring and predicting hurricanes and other extreme weather events
• Improved forecasting abilities for natural hazards, including floods, droughts and landslides.
• Enhanced numerical prediction skills
• Improved agricultural crop forecasting and monitoring of freshwater resources

 

 

IDL provides building blocks that scientists can use to help them perform research and aid in discovery including language constructs, file access libraries, data analysis libraries, and visualization toolkits.