Gulfstream Jet Prop Commander (AC690A)

The Gulfstream Jet Prop Commander 1000 (AC-695A) is a stable high-wing, pressurized, twin-engine turboprop aircraft that is suitable for a variety of missions. Standard configuration allows for mission equipment, two pilots and one observer. However, the aircraft can be configured for two scientists/observers and mission equipment in the cabin. NOAAs AC-695A Jet Prop Commander is typically utilized by the National Weather Service (NWS) National Operational Hydrologic Remote Sensing Center (NOHRSC).

The AC-695A jet prop commander aircraft is used by the National Operational Hydrologic Remote Sensing Center (NOHRSC) to conduct aerial snow survey operations in the snow-affected regions of the United States and Canada. During the snow season (Oct May), snow water equivalent measurements are gathered over a number of the 2000+ pre-surveyed flight lines using a gamma radiation detection system mounted in the cabin of the aircraft. During survey flights, this system is flown at 500 feet above the ground at ground speeds ranging between 100 and 120 knots. Gamma radiation emitted from trace elements of potassium, uranium and thorium radioisotopes in the upper 20 cm of soil is attenuated by soil moisture and water mass in the snow cover. Through careful analysis, differences between airborne radiation measurements made over bare ground is compared to that of snow-covered ground. The radiation differences are corrected for airmass attenuation and extraneous gamma contamination from cosmic sources. Airmass correction is accomplished using output from precision radar altimeter and pressure sensors mounted on and within the aircraft. Output from the snow survey system results in a mean areal snow water equivalent value within +/- one cm. Information collected during snow survey missions, along with photographic data, is used by the National Weather Service (NWS), River Forecasting Centers (RFCs) and other agencies to forecast river levels, water flow, and potential flooding events due to snowmelt water runoff.

STANDARD AIRCRAFT SPECIFICATIONS

Additional Standard Equipment

Airborne Snow Measurements Help Forecast Flooding and Water Supply

Snow is a significant element in the United States. The devastating snowmelt flood of 1997 on the Minnesota River and Red River of the North caused damage in excess of $4.0 billion and constituted the most expensive natural disaster, on a per capita basis, in U.S. history. The economic impact of snow on the farming, hydroelectric power, and recreation industries alone as been estimated to be $18.9 billion annually. Clearly, snow is a critical component in the nations infrastructure.

Consequently, the National Operational Hydrologic Remote Sensing Center (NOHRSC) in the U.S. National Weather Service (NWS) and the Aircraft Operations Center (AOC) in the Office of Marine and Aviation Operations (OMAO) of the National Oceanic and Atmospheric Administration (NOAA) has maintained an Airborne Gamma Radiation Snow Survey Program across the country for over 20 years. Snow survey aircraft are used to make near real-time, reliable, airborne snow water equivalent measurements across the country during the winter. The airborne snow water equivalent data are used by the NWS Hydrologic Services Program when issuing spring snow melt flood outlooks, water supply outlooks, and river and flood forecasts for the nation.

NOAA Corps Officers and pilots based at AOC use the survey aircraft to make measurements of natural terrestrial gamma radiation emitted from the potassium, thorium, and uranium radioisotopes in the upper 20 cm of soil. A network of 2170 operational flight lines has been established covering portions of 31 states (including Alaska) and 8 Canadian provinces. A one-time background measurement of natural terrestrial radiation, with no snow, is used to calibrate each flight line that is typically 15-20 km long and 300 m wide. Water mass in the snowpack attenuates, or blocks, the terrestrial radiation. Consequently, it is possible to make a subsequent airborne radiation measurement over a calibrated flight line, with a snowpack, and infer the snow water equivalent on the ground with a root mean square error of 0.81 cm in agricultural environments, 2.31 cm in forested environments, and 3.50 cm in montane environments.

The NOHRSC uses a piston-powered, twin-engine, cabin-class, Aero Commander (AC500S) in the Upper Midwest and in the East and a turboprop, twin-engine, cabin-class Jet Prop Commander (AC695A) in the West and in Alaska to make simultaneous airborne snow water equivalent measurements across the country almost continuously from early January through mid-April. During heavy snow years in the West, airborne data collection can extend into May and early June to assess the high elevation snowpack remaining in the alpine and above the established ground-based snow water equivalent measurements systems where the snowpack has melted out. During operational airborne snow surveys, the radiation data are processed in the aircraft in real-time and the snow water equivalent estimates are telemetered up to three times daily from each aircraft to the NOHRSC office in Minneapolis. Immediately upon receipt at the NOHRSC, the data are automatically processed and formatted, sent to the NWS satellite broadcast network, and received by each of the NWS field offices in less than 5 minutes of transmission from each survey aircraft.

More information about NOAA aircraft can be found at NOAA's Aircraft Operations Center.

National Weather Service National Operational Hydrologic Remote Sensing Center Office of Water Prediction 1735 Lake Drive W. Chanhassen, MN 55317
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