For six weeks in Ontario, Canada, scientists and engineers lead a field campaign to study the science and mechanics of falling snow. The datasets retrieved will be used to generate algorithms which translate what the GPM Core satellite "sees" into precipitation rates, including that of falling snow. Ground validation science manager Walt Petersen gives a summary of the GCPEx field campaign. Field campaigns are critical in improving satellite observations and precipitation measurements.
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Walt: We just returned from the GPM Cold Season Precipitation Experiment held in Ontario, Canada. And it was a very successful experiment. We collected the bulk of the data that we went up there to get, and I think that everybody is very happy with the dataset. I would say that it did not snow across the norther tier of the United States and Southern Canada as much as we had hoped it would this year, but surprisingly enough, even given the relative lack of snow that we had, we got all the events that we basically wanted. One of the objectives for this field campaign was to test the range of snowfall intensities that occur. And the idea being there that we would be able to sort of find where it is in that spectrum of events that we would actually be able to detect falling snow from space with the GPM Core satellite.
[ jet engine ]
Through the duration of the campaign we went the full six weeks using all the aircraft hours that were available to us on the DC-8. We flew about 14 missions, for a total about 75 flight hours I sort of assumed we would show up and basically burn out our flight hours in a very short time up there in frequent heavy snowfall events, and what actually transpired is that we ended up using the entire duration of the field campaign to get our datasets because the snow events were sort of spaced fairly regularly and were not that heavy and we kept wanting to get the heavier event, and it took a while to get that.
Steve: As you can see it's snowing pretty good this morning at the CARE site. Pretty nice large aggregates. It's exactly what we're looking for and it just keeps coming down.
Walt: So we've completed the GCPEx experiment in terms of being on the ground and collecting the data. Now a phenomenal effort actually goes into quality controlling all of the data we collected. That is, to make sure that all of those datasets that we collected are usable, there's no bad data in the datasets, and that has to be done for a huge number of ground instruments that were deployed, both radars direct measurements of snowfall using gauges, particle imaging systems, all of those data on the ground.
And then you have to move to the aircraft data, which is also very complex because you've got several different probe types that were flying in the clouds, looking at different aspects of the precipitation and all of that data has to be quality controlled. And finally you have the satellite simulator, or the DC-8, that carried the radiometer, the COSMIR radiometer and the APR-2 radar. All of those data have to be--and we're talking gigabytes and terabytes-- of data that has to be quality controlled. That will take on the order of six months to a year to accomplish. And that connection in between what I measured during this field campaign to what I think I'm going to see in space essentially encompasses the development process of making an algorithm to retrieve the snowfall from space.
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