NASA will launch an airborne science lab aboard a DC-8 plane above Canadian snowstorms next week to measure snowfall from space.
"Snow is notoriously hard to measure as it falls," said NASA scientist Walter Petersen. "Snowflakes contain varying amounts of air and water, and they flutter, wobble and drift as they leave the clouds."
Scientists can measure overall water content by determining how "wet" a snowflake is. That information is crucial for cities where a wet, heavy snow can shut them down. Melted snow is also a key source of fresh water in many areas.
NASA's Cold-season Precipitation Experiment will measure light rain and snow in Ontario from Jan. 17 to Feb. 29.
The field campaign is designed to improve satellite estimates of falling snow and test ground validation capabilities in advance of the launch of the GPM Core satellite in 2014.
"We will be looking at the precipitation and the physics of precipitation, such as snowflake types, sizes, shapes, numbers and water content," Petersen said. "These properties affect both how we interpret and improve our measurements."
The Ontario region is ideal for the campaign because it is prone to both lake effect snow squalls and widespread snowstorms. The DC-8 may also fly over blizzards along the northeastern United State if these occur during the time period.
The plane will fly out of Bangor, Maine, carrying radar and a radiometer that will simulate the measurements to be taken from space by GPM. At an altitude of 10 kilometres, the DC-8 will make multiple passes over an extensive ground network of snow gauges and sensors at Environment Canada's Centre for Atmospheric Research Experiments north of Toronto.
At the same that the DC-8 is flying above the clouds, two other aircraft, one from the University of North Dakota and another from Canada, will fly through the clouds, measuring the microphysical properties of the raindrops and snowflakes inside.
Advanced ground radar will scan the entire air column from the clouds to the Earth's surface.
"These multiple measurements of snowfall provide a complete picture, a complete model, of the snowfall process from top to bottom," Petersen said.
The campaign is part of the Global Precipitation Measurement (GPM) satellite mission, which will provide worldwide observations of snow and rain from space every three hours. It is the first mission to detect falling snow from space.
GPM's core satellite will orbit Earth at a 65-degree inclination, covering the world from the Antarctic Circle to the Arctic Circle.
GPM will carry a microwave radiometer and a dual-frequency precipitation radar that distinguishes a snowflake's size and shape, which affects how much water it holds. Knowing these microphysical properties will lead to more accurate estimates of rain and snowfall, especially during winter and at high latitudes where snow is the dominant form of precipitation.