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Praying for rain. The GPM rainfall measurements from the ground-up perspective


So, what if I told you that the water you drink today is the same water dinosaurs drank over one hundred million years ago? Yep, the same amount of water has been circulating the globe in what we call “The Hydrologic Cycle” (also known as the Water Cycle). But don’t worry, you will not catch some dinosaur-disease by drinking it. Water in the Hydrologic Cycle has the ability to evaporate from the land and ocean surfaces and travel large distances as water vapor, only to fall down on the ground as precipitation (rain and snow). The same water later travels on the surface as streams and rivers or underground - all the way back to the ocean. These processes help remove impurities from the water and make it clean again!

 

We drink what they used to drink
We drink what they used to drink
The Water Cycle

So, how can we learn more about how all this water keeps traveling around the globe? We can use a number of different instruments to study the Hydrologic Cycle. Some instruments are simple, like a rain gauge. A basic rain gauge may look like a glass or a bucket, and it can provide a great way to study how much water falls on the ground as rainfall. Other instruments can be very complex and expensive, like satellites. The Global Precipitation Measurement (GPM) Mission satellite has been designed to observe rain and snow around the globe. But this satellite travels over 250 miles above the Earth – so how can it see anything from so far away? Can you see anything when you are 250 miles (400 km) away? Not with human eyes. So how does a satellite detect something so small as a raindrop or a snowflake from that distance? How can we learn if satellites can detect and estimate precipitation?

 

GPM Satellite
GPM Satellite
Simple rain gauge
Simple rain gauge
Dual rain gauge
Dual rain gauge

 

I spent almost three years working at NASA in the GPM Ground Validation group, and as part of my responsibilities I got to measure on the ground what the GPM satellite can see from space. NASA learns about how well satellites can measure rainfall by conducting field campaigns. Field campaigns usually last for a few weeks and gather in one place a wide range of precipitation measuring instrumentation ranging from rain gauges and disdrometers (instruments that can measure single rain drops) to weather radars and even airplanes! And of course the GPM satellite traveling 250 miles (400 km) above us is there too! Having all the instruments in one place allows scientists to create a very unique data sample by recording rainfall or snowfall in a number of ways. Of course we need a lot of people to first design and later conduct the campaign. It is a long process and requires a lot of effort to plan and make sure everything works in the end. After the campaign scientists from all around the world can access the data and study it. The best part about my job at NASA was that I got to travel…a lot.

 

As you may already know, there are places in the U.S. where it almost never rains. On the other hand there are some places where it rains a lot. So which one is better to study rainfall? Yes, NASA Ground Validation field campaigns are always at locations and seasons when we can expect a lot of rainfall and a lot of good data.  

 

How does a “normal day” during a Ground Validation field campaign look like? It depends on the weather! Unlike most people, we love when it rains, because this is when we can gather data and with a lot of good data we can have a successful field campaign. On a rainy day everyone is busy.  Technicians need to make sure that all instruments stay in operational condition. We need to coordinate between groups (ground instrument groups, aircraft group, radar group, etc.) to make sure we complete the objectives designated by the operations center. Every campaign has an operations center which is responsible for coordinating the work of all the people involved…think of a general during a battle…we always have a “general” during the campaigns.

 

Maintenance of 2DVD during field campaign in Iowa
NPOL radar

On a dry day when no precipitation is expected it is our time to check on instruments, perform necessary maintenance and maybe look at the data collected during rainy rays. It is also a great time for visitors. During every field campaign we have a large number of people from the local community visiting us. People are usually curious when they see something they are not familiar with (like our massive NPOL radar – look at the picture above), so they are always welcome to come and ask questions and tour our facilities.

Rainy days can be very busy and the campaign is a 24hours-7-days-a-week activity so it is nice to get a quiet day once in a while when everyone can get some rest and prepare for another storm. Sometimes Mother Nature can test our patience and we don’t see any rain for a long time….so the only other think we can do during those dry days is…pray for some rain.

Students from a local school visiting NASA facility
Students are learning about precipitation and radars

 

Every campaign I participated in was a great learning experience and a lot of fun. Learning about rainfall, snowfall and the Hydrologic Cycle is very important because to understand how the global climate is changing we need to first understand how water circulates around the globe. So make sure you come back and learn more about how NASA, together with scientists around the world is doing just that!

 

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