Measuring rainfall from space with satellites.
The next section gives you a bit of theoretical background on remote sensing derived precipitation estimations. Please read the text and write down the answers in a word document.
There are a number of standard products offering precipitation estimates in a regular basis that can be used for water planning and management purposes. Satellite derived products have the advantage of providing data dense solutions covering vast areas, as compared to gauge measurements, which only provide point measurements. As such, they provide an alternative to sparse rain gauge networks for assessing the spatial distribution of precipitation. The products can be freely obtained from the Internet and are available for a range of temporal resolutions.
Question 2.1: What method(s) are used in more traditional approaches to estimate precipitation over a river basin?
The Tropical Rainfall Measuring Mission (TRMM), launched by NASA and JAXA in 1997, used both active and passive microwave instruments to measure rainfall in the tropics. It also provided a foundation for merging rainfall information from other satellites. TRMM has shown the importance of taking observations from a non-Sun-synchronous orbit at different times of the day, between observations by polar orbiting sensors at fixed times of the day, to improve near real-time monitoring of hurricanes and accurate estimation of time-accumulation of rain volume. The GPM Core Observatory continues this sampling from a non-Sun-synchronous orbit and extends coverage to higher latitudes to provide a global view of precipitation [ref].
Question 2.2: What is the difference between active and passive instruments?
Question 2.3: Explain the difference between a non-Sun-synchronous orbit and geostationary satellites.
Question 2.4: What are the advantages of geostationary satellites in terms of temporal resolution. What are the disadvantages in terms of spatial resolution?
The TRMM satellite contains a number of instruments. The Precipitation Radar (PR), TRMM Microwave Imager (TMI), Visible and Infrared Scanner (VIRS), Clouds and the Earth’s Radiant Energy Sensor (CERES) and Lightning Imaging Sensor (LIS).
Question 2.5: Go to this and this website and read the description of the different instruments. Explain in your own word what the TMI sensor does?
The Global Precipitation Measurement (GPM) mission is an international network of satellites that provide the next-generation global observations of rain and snow. Building upon the success of the Tropical Rainfall Measuring Mission (TRMM), 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. Through improved measurements of precipitation globally, the GPM mission is helping to 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 [ref].
The following movie gives more information on TRMM and GPM.
Question 2.6: What benefits can bring the GPM mission to water management practices in Vietnam? Give three:
The following movie shows you the orbit of the GPM satellite:
Question 2.7: GPM has a revisit time of 3 hours, while TRMM has a revisit time of about 12 hours. Why is it important to have high revisit times for precipitation monitoring?
Question 2.8: This website gives a description on how the 3B43 and 3B42 are created. How can NASA create 3-hourly precipitation maps with revisit times of 12 hours?