THE USGS AERIAL PROFILING OF TERRAIN SYSTEM 
Edward J. Cyran and William H. Chapman 
U.S. Geological Survey 
526 National Center 
Reston, Virginia 22092 
U.S.A. 
ABSTRACT 
The Aerial Profiling of Terrain System (APTS), developed under a contract 
for the U.S. Geological Survey by the Charles Stark Draper Laboratory, has 
been used to perform a series of application tests and to complete a major 
terrain profiling project in the Great Salt Lake Desert area, Utah. 
The APTS, designed to be carried in a relatively small aircraft such as a 
Twin-Otter, consists of an inertial measuring unit (IMU), a laser tracker, 
a laser profiler, a video imaging system, supporting electronics, and a 
computer. The IMU and laser tracker provide an accurate three-dimensional 
reference frame based on the local datum. The laser profiler measures 
accurate ranges to the topography from the reference platform. The on- 
board computer serves as a system controller and a data collector and 
processor while navigating the aircraft during data collection activi- 
ties. A video system records the ground image below the aircraft during 
profiling. 
To develop operational procedures and to demonstrate effectiveness in 
earth science data collection, the system was tested in several applica- 
tions. These applications included positioning water wells and measuring 
water surface elevations along the Charles River in Massachusetts, perform- 
ing map accuracy surveys of four 7.5-minute topographic maps, measuring the 
surface elevation of over 100 kettle ponds near Plymouth, Massachusetts, 
and surveying ground points using the laser tracker. With the completion 
of the applications tests, the system was flown to the Great Salt Lake 
Desert area, where it was used to successfully measure approximately 1,200 
miles of profiles. Comparisons at crossing profiles from this project 
indicate root mean square difference of 1.28 feet and an average absolute 
difference of 0.91 feet. 
INTRODUCTION 
The Aerial Profiling of Terrain System (APTS), developed by the Charles 
Stark Draper Laboratory for the U.S. Geological Survey (USGS), has under- 
gone field testing during the last 2 years to determine its effectiveness 
as a terrain measuring instrument. The APTS is an airborne inertial 
surveying system supplemented with laser instruments which provide measure- 
ments for transferring position and elevation coordinates to the ground. 
It consists of an inertial platform, laser tracker, laser profiler, and 
video imaging system. When performing profile surveys, the inertial navi- 
gation system provides continuous position and elevation information for 
the aircraft, and the laser profiler measures ground profiles relative to 
the aircraft. To control the accumulated errors of the inertial navigation 
system, the laser tracker periodically provides independent position infor- 
mation by measuring range and direction to retroreflectors prepositioned 
on the ground. During performance evaluation test flights, APTS 
  
Publication authorized by the Director, U.S. Geological Survey. 
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