Patrick Gatlin says his work measuring the height and width of raindrops using ground instruments provides an accuracy baseline that is then scaled up to ground radar and then to satellite measurements.
He is co-author of a paper on the topic (Tokay, Ali, Walter A. Petersen, Patrick Gatlin, Matthew Wingo, 2013: Comparison of Raindrop Size Distribution Measurements by Collocated Disdrometers. J. Atmos. Oceanic Technol., 30, 1672–1690; http://dx.doi.org/10.1175/JTECH-D-12-00163.1).
“That’s really the whole purpose of measuring raindrops, is for remote sensing purposes,” Gatlin says. Scaling up accuracy from a small sensor on the ground to large sections of the Earth being observed from space requires very accurately calibrated instruments. “Our ability to correctly depict rainfall using a sensor in space is closely tied to knowing how precipitation varies, right down to the individual raindrop and snowflake size.”
Perfecting ground-level instrument observations, enlarging those to encompass ground-based radar and then going even larger to develop accurate satellite measuring instruments is the best way to reduce error as the area under observation increases. “Before we invest in all this satellite instrumentation,” Gatlin says, “let’s make sure we’ve got it right.”
A coming big step in scaling up precipitation forecasting is NASA’s planned launch of its Global Precipitation Measurement (GPM) satellite toward the end of February. UAH is a mission contractor, headed at the university by Dr. Larry Carey, an associate professor of atmospheric science, and involving UAH Earth System Science Center research scientist Matt Wingo, who is working with NASA at their flight facility in Wallops Island, Va.
“UAH designed the platform for some of the ground-based instruments that will validate the information from the satellite,” says Gatlin.
Carrying an advanced radar/radiometer system to measure precipitation from space, the GPM is the core of what will be a global network of measuring satellites that will provide next-generation global observations of rain and snow. It will 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 will help to advance 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 precipitation information.
In his own research, Gatlin has ranged from Iowa and Oklahoma to Canada, Finland, Italy and France. Rather than raindrops, the Canadian research was designed to collect snowflake images in order to improve the accuracy of measuring devices for snowfall.
In each locale, an integrated network of ground-level measuring devices have been deployed, like the Parsivel2, a disdrometer that measures the particle size and velocity of raindrops falling through a laser. Also in use are two-dimensional video disdrometers, which use two video angles to create 2-D pictures that enable determination of raindrop shapes. A video disdrometer on loan from frequent research collaborator Colorado State University is located on the UAH campus behind Cramer Hall.
During a field study, the instruments on the ground take measurements while a plane flies through the clouds to collect actual raindrop information and another flies high above the clouds with remote sensing equipment to mimic satellite radar detection. Results from all the measurement methods are compared.
Enhanced satellite-based precipitation measurements will improve both rainfall and snowfall predictions on a global scale, Gatlin says. “We’ll be measuring rain and snow in some areas where we’ve never measured it before.” The ability to better measure raindrop size also can have impact on severe weather forecasting, as small raindrops lead to higher evaporation rates that have been correlated with larger and more forceful microbursts by UAH’s Dr. Kevin Knupp and others.
Gatlin is about to finish up a global study focusing just on very large raindrops 5 millimeters in size and larger. These drops are difficult to capture in the small measuring area afforded by measuring instruments, and so their observation is rare. Gatlin says out of 224 million drops he has researched, only 8,000 have been 5 mm or larger.
“Even though large raindrops can have the greatest impact on radar measurements, we don’t have a good idea of their concentration,” he says. “What I’ve been doing is bringing together all the raindrop data bases that have collected various types of rainfall data using the same techniques.”
Interestingly, while Sumatra holds the honor of having the greatest number of large drops overall, the largest drop collected in his study fell through a measuring device at the UAH campus. It measured 9.1 mm and was formed in a hailstorm when a falling piece of hail melted before landing.
Patrick Gatlin | Newswise
In the Southern Ocean, a carbon-dioxide mystery comes clear
04.02.2016 | The Earth Institute at Columbia University
Several metre thick ice cocktail beneath coastal Antarctic sea ice
04.02.2016 | Alfred-Wegener-Institut, Helmholtz-Zentrum für Polar- und Meeresforschung
Automobiles increase the mobility of their users. However, their maneuverability is pushed to the limit by cramped inner city conditions. Those who need to...
Advance in biomedical imaging: The University of Würzburg's Biocenter has enhanced fluorescence microscopy to label and visualise up to nine different cell structures simultaneously.
Fluorescence microscopy allows researchers to visualise biomolecules in cells. They label the molecules using fluorescent probes, excite them with light and...
NASA's follow-on to the successful ICESat mission will employ a never-before-flown technique for determining the topography of ice sheets and the thickness of sea ice, but that won't be the only first for this mission.
Slated for launch in 2018, NASA's Ice, Cloud and land Elevation Satellite-2 (ICESat-2) also will carry a 3-D printed part made of polyetherketoneketone (PEKK),...
In the last decades, sea level has been rising continuously – about 3.3 mm per year. For reef islands such as the Maldives or the Marshall Islands a sinister picture is being painted evoking the demise of the island states and their cultures. Are the effects of sea-level rise already noticeable on reef islands? Scientists from the ZMT have now answered this question for the Takuu Atoll, a group of Pacific islands, located northeast of Papua New Guinea.
In the last decades, sea level has been rising continuously – about 3.3 mm per year. For reef islands such as the Maldives or the Marshall Islands a sinister...
The ‘Internet of Things’ is growing rapidly. Mobile phones, washing machines and the milk bottle in the fridge: the idea is that minicomputers connected to these will be able to process information, receive and send data. This requires electrical power. Transistors that are capable of switching information with a single electron use far less power than field effect transistors that are commonly used in computers. However, these innovative electronic switches do not yet work at room temperature. Scientists working on the new EU research project ‘Ions4Set’ intend to change this. The program will be launched on February 1. It is coordinated by the Helmholtz-Zentrum Dresden-Rossendorf (HZDR).
“Billions of tiny computers will in future communicate with each other via the Internet or locally. Yet power consumption currently remains a great obstacle”,...
02.02.2016 | Event News
26.01.2016 | Event News
26.01.2016 | Event News
05.02.2016 | Life Sciences
05.02.2016 | Materials Sciences
05.02.2016 | Physics and Astronomy