National Aeronautics and Space Administration

Wallops Flight Facility

Instruments

The ATM instrument suite is a versatile package of airborne science instruments that can be tailored to many different science applications and platform configurations. The ATM instrument suite has collected high-precision topographic data from a wide variety of platforms, including the NASA P-3, a Chilean Navy P-3, a US Navy P-3, NOAA P-3, the NASA DC-8, the NCAR C-130, the NASA C-130, the NASA HU-25C, and a half-dozen Twin Otters. The ATM instrument suite has been adapted to various platforms, and typically operates at altitudes from 1,500 ft/450 m above ground level (AGL) (optimally) up to 35,000 ft/10000 meters. Part of the instrument suite is ATM’s precision aircraft guidance system that allows to steer the aircraft precisely on the desired path to obtain overlapping data for change detection versus prior ATM surveys or spacecraft underflights. Once engaged, the ATM system steers the aircraft by comparing its GPS position with a pre-programmed desired track, and generating the appropriate signal for the autopilot to keep the aircraft aligned with the target track typically within 1.8 m of the ideal flight path. The main component of the instrument suite are two conically-scanning laser altimeters that independently measure the surface topography of a swath beneath the aircraft at a 15° and 2.5° off-nadir angle respectively. ATM instrument suite consists of:

Instrument Scan angle
(degrees)
Wavelength PRF
(Hz)
Pulse Width
(ns)
Swath width
at 450m AGL
Footprint size
at 450m AGL
ATM 6d-T7 2.5 532 10,000 1.3 40 m 0.64 m
ATM 6c-T7 2.5 1064 10,000 1.3 40 m 0.91 m
ATM 6a-T6 15 532 10,000 1.3 245 m 0.61 m

The ATM T7 transceiver is a dual color laser with co-located green and near-infrared laser beams. Like most modern airborne laser altimeters, the ATM systems record the full waveform of the transmitted and received laser pulse. The ATM laser altimeters have an accuracy of better than 6 cm [​Martin et al.​, 2012] which has been confirmed independently in the interior of continental ice sheets for 4 generations of ATM transceivers [​Brunt et al.,​ 2017; ​Brunt et al.​, 2019].

Schematic of ATM-T7 dual-color transceiver

 

The ATM-T6 and ATM-T7 transceivers, with associated hardware racks, installed on the NASA G-V.