Rockwell Aero Commander (AC-500S)

The Rockwell Aero Commander (AC-500S) is a versatile and stable high-winged twin piston-engine aircraft that is suitable for a variety of missions. Standard configuration allows for mission equipment and two pilots. However, with the scientific packages removed, seating for five additional passengers may be installed. NOAA's two aero commanders are utilized primarily as aerial survey platforms for visual verification of aeronautical charts, high-resolution aerial photography, and snow water equivalent and soil moisture content measurements. Additionally, the aircraft has been used in biological investigations, such as algal bloom measurements and sea turtle population assessments, and post-hurricane and severe flood damage assessment photography.

STANDARD AIRCRAFT SPECIFICATIONS

The aircraft seating arrangement can accommodate a maximum of five passengers in addition to the two flight crew members. Two single seats can be installed just behind the pilot and copilot seats and a bench seat for three people can be placed at the aft end of the cabin. Passengers have access to external viewing through any of four cabin windows, two on each side of the aircraft fuselage at eye-level. Each of the forward square-shaped cabin windows measures 16 inches wide by 16.375 inches high. The aft cabin windows, which are oblique quadrilateral in shape, measure 16.75 inches wide by 14.5 inches high at the center of the window. Partial viewing is possible through the cockpit forward windows and cockpit brow windows.

Snow Survey Platform (N51RF)

An AC-500S Aero 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 (January-April), 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. In the fall season, the same equipment is used to measure the soil moisture before snowfall is expected, and to measure the background radiation signature of new flight lines. 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 the earth is attenuated by soil moisture in the upper 20 cm of soil 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. The airmass correction is calculated using the output from precision temperature, 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 centimeter. Data collected during snow survey missions, including observed ground and weather conditions, are used by the National Weather Service (NWS) and other agencies to forecast river levels and potential flooding events due to snowmelt water runoff. Hydroelectric power interests and other water supply managers also use the data to regulate water storage and delivery.

Aircraft Modifications to N51RF:

• Customized tail cone with downward looking remote video camera
• Precision temperature probe mounted on the top of the fuselage
• Trimble 3000 GPS with output port
• Radar altimeter with analog output

Snow Survey Platform (N51RF)

The gamma detection system is composed of the following equipment:

• Crystal Box (2.5 ft. x 2 ft. x 1.5 ft., 316 lbs.)
• 7 NaI-Tl scintillation detector crystals
• 7 photomultiplier tubes
• 7 pre-amplifiers
• Equipment Rack (162 lbs.)
• Nuclear Instrumentation Module (NIM) bin with 12 volt DC power supply
• 1 ORTEC 920-8 multi-channel buffer
• 2 summing amplifiers (UP and DOWN)
• 1 analog module (converts temperature sensor, pressure sensor, and radar altimeter data to digital form)
• 1 Bertan high voltage power supply
• 1 ORTEC 6 volt power supply
• PICODAS 486 computer (PDAS 1000)
• KEITHLEY METRABYTE DAS 802 card for Analog box input
• ORTEC 918 card for input from the multi-channel buffer
• Double Talk PC Speech Synthesizer
• Analog pressure sensor
• DC-to-AC inverter, power strip, and power circuit breaker switch
• Peripheral Equipment
• Radar altimeter
• Analog temperature sensor

Multi-Purpose Survey Platform (N47RF)

Aero Commander N47RF is configured to conduct a variety of remote sensing missions. The aircraft has been modified with an 18-inch diameter, belly-mounted camera hatch. This hatch has a hydraulic door which can be opened and closed in flight. When closed, the door seals tightly to protect any instrumentation mounted in the hatch, and to provide a quieter cabin environment. When open, the door swings out approximately 160 degrees to provide an unobstructed view of the earth below. Using different mounts, a variety of sensors can be installed above the "hole" to provide remote sensing data. Additionally, the relatively large diameter of the opening can, in some cases, allow for the simultaneous mounting of several complimentary sensors. The aircraft cabin has a 28v DC scientific power drop and a standard equipment rack to house data collection computers, video monitors, GPS systems, or any other electronic support equipment.

This aircraft was acquired in 1982 to conduct visual and photographic surveys of aeronautical charts. In 2000, the FAA assumed responsibility for these surveys. However, the photographic component of this mission is still performed by N47RF. This mission involves the aerial photography of air traffic obstructions such as towers, stacks, and buildings. Two pilots perform the mission with one flying the aircraft and the other operating the RC-8 aerial camera system. The RC-8 is capable of taking a series of high-resolution 9-inch x 9-inch photographs with a pre-selected overlap. These photo series are then used to extract height and location information for each obstruction. In addition to obstruction photography, the RC-8 can and has been used for post-disaster photography to document the damage caused by hurricanes, floods, fires, etc.

Besides the RC-8 camera system, the aircraft has also been flown with numerous other sensor systems including hyperspectral imagers, infrared.video cameras, and digital still cameras. These systems have been utilized to detect red tides, measure the health of kelp forests and coral reefs, and to study the effects of wind and current on the oceans surface.

When not employing remote sensors, the aircraft is an outstanding visual survey platform as well. With the high-wing design pilots are afforded very good visibility. In addition, forward, rearward, and downward visibility is improved by two bubble windows installed in the forward cabin area. The enhanced visibility, as well as the Aero Commander's ability to fly low at slow airspeeds while remaining highly maneuverable, makes this aircraft a capable tool for survey or patrol duty. Past projects include Right Whales surveys off the New England coast, Turtle Surveys off the Mid-Atlantic coast, and fish surveys along the Gulf Coast.

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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