Gulfstream Turbo Commander (AC690)

The Gulfstream Turbo Commander (AC-690) is a stable high-winged twin, pressurized turboprop aircraft that is suitable for a variety of missions. The standard configuration allows for mission equipment, two pilots, and one photographer. However, with all seats installed, five scientists/technicians may be accommodated in the cabin. NOAA's AC-690 Turbo Commander is utilized by the NGS Remote Sensing Division and the NOHRSC (National Operational Hydrologic Remote Sensing Center).

The NGS conducts aeronautical surveys requiring collection of stereophotographic and remotely sensed data. These surveys facilitate coastal mapping, airport obstruction charting, photobathymetry, photogeodesy, boundary determination, and coastal wetlands mapping. Depending on the scale of imagery required, missions are flown at altitudes of 1000 to 24,000 feet above ground level using kinematic GPS survey techniques. Through post-processing methods, such as photo-interpretation and photogrammetric measurement, the NGS uses the data to develop NOAA charting products.

The AC-690 is utilized by the NOHRSC to conduct airborne snow surveys using a gamma detection system. The system measures natural terrestrial gamma radiation over specific flight lines for the purpose of determining soil moisture and snow water equivalent. This data is used in near real time by hydrologists and water supply managers to make better flood forecasts and water supply predictions. NOAA's AC-690 is most useful in collecting airborne gamma data in the mountains of the western U.S., Canada, and Alaska, where the high power and pressurization features of the aircraft increase efficiency and safety.

STANDARD AIRCRAFT SPECIFICATIONS

The following modifications and installations have been
made to the AC-690:

• Belly camera port with hydraulically actuated hatch
• Wild RC-10 aerial camera
• Video camera mount through belly camera port
• Daedalus multi-spectral scanner
• Gamma radiation detection system
• Color weather radar
• Scientific AC power inverter
• UHF radio antenna for monitoring real-time tide gauge broadcasts for tide-coordinated photography
• Trimble TNL 3000 cockpit mounted GPS
• Computer-controlled navigation system (CCNS-4) flight management system for precision guidance, positioning and data acquisition
• Secondary external GPS antenna with 12-channel survey quality Trimble GPS

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 Turbo Commander (AC690A) 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.

Further information regarding the snow survey program can be obtained by accessing the National Operational Hydrologic Remote Sensing Center, Office of Hydrology website at http://www.nohrsc.nws.gov