486
July 2016
PHOTOGRAMMETRIC ENGINEERING & REMOTE SENSING
signed to stimulate the development of the art of aerial photo-
grammetry in the United States. Practicability is the essence
of the Award and is the basis for the review of all candidates.
Donor:
The ASPRS Foundation and Lockheed Martin
The award consists of a silver presentation plaque mounted on
a walnut wood panel and an engraved plaque.
ASPRS Outstanding Technical Achievement
Award (OTAA)
Charles C. Counselman III
for making accurate position information available to all
The ASPRS awards its 2016 OTAA to Professor and Dr.
Charles (Chuck) Counselman of MIT for making it possible for
everyone to determine position coordinates accurately from
radio signals received from earth-satellites such as those of
the Global Positioning System, or “GPS.”
The path to accurate positioning for all became visible
during World War II, with the development of radio- or ra-
dar-based methods of positioning and navigation, especially
Loran. GPS is basically a Loran system with radio transmit-
ters orbiting the Earth instead of fixed on shorelines. GPS is
more accurate because its radio signals can travel along clear
lines-of-sight; whereas Loran signals must follow the earth’s
curved surface
via
ground- and/or ionosphere-guided modes of
propagation.
In 1981, GPS was being developed by the U.S. Air Force as
a weapon system, a “force enhancer.” To keep an enemy from
using GPS against us, all GPS signals were encoded and the
code keys would be military secrets, not available to anyone
outside the Department of Defense (the “DoD”), a few other
U.S. government agencies, and allied military forces.
Independently, in 1981, Professor Counselman invented a
method and system for determining position from GPS sig-
nals without knowledge of the GPS codes. Recognizing the
potential for hostile use of his inventions, he disclosed them to
the Air Force. He was told to limit further disclosure and to
register with the Office of Munitions Control, but he was en-
couraged to develop his inventions because they promised to
reduce the uncertainty of GPS-based position determination
by a factor of one thousand.
In 1982, the Air Force found another reason to like Coun-
selman’s inventions. The U.S. Congress had begun to press
the DoD to make GPS available to the general public. Coun-
selman gave the DoD a way to do this while continuing to
defend against hostile use.
Counselman’s GPS technology was derived from radio-as-
tronomical techniques he had developed and applied ten years
earlier to determine the positions of quasars (natural, extra-
galactic, radio sources)
[
Ref. 1
]
; to test Einstein’s General Theory
of Relativity
[
2
]
; to establish selenodetic control for photogram-
metry of the Moon
[
3
]
; to track the Apollo Lunar Roving Vehi-
cles
[
4
]
; and, in 1980, to determine wind speeds and directions
in the atmosphere of Venus
[
5
]
. His method was to determine
position from “doubly differenced” phase observations. The
phases of radio signals emitted simultaneously by different
sources and received simultaneously (except for propaga-
tion-delay differences) by different receivers were differenced
between the sources and between the receivers. Thus, un-
known phase shifts associated with individual sources, and
with individual receivers, were canceled; so the relative posi-
tions of the sources and/or receivers could be determined with
exquisite accuracy.
When he learned of the Air Force’s NAVSTAR system
(later renamed “GPS”), Professor Counselman knew that his
doubly-differenced-phase technique, applied to GPS, would
determine relative-position vectors with millimeter- to centi-
meter-level accuracy.
[
6
]
He would need receivers that were
adapted to the GPS signal structure and that measured the
phases of the carrier and subcarrier waves implicit in GPS
signals received simultaneously from multiple satellites.
To keep the phases of signals received from different satel-
lites from being shifted differently by a receiver, he invented
a receiver architecture in which a composite of signals coming
from multiple satellites was digitized before different satel-
lites’ signals were separated. Then, by synchronous, parallel,
digital processing, the different satellites’ carrier and subcar-
rier phases could be determined, free of error due to inter-sat-
ellite differences.
Counselman and a former MIT colleague themselves fund-
ed the development of a practical hardware-software system
for accurate positioning, using GPS satellite signals, without
knowledge of the GPS codes. Position was determined from
doubly-differenced phase observations. This system, the Mac-
rometer
®
Interferometric Surveyor, was announced in Feb.
1982
[
7
]
and was tested by the multi-agency Federal Geodetic
Control Committee in Jan. 1983
[
8
]
. Macrometer systems were
bought by the U.S. National Geodetic Survey and by geodet-
ic surveying firms in the USA and Germany; and they were
used on five continents. Macrometer systems have been in
the Scientific Instruments collection of the Smithsonian Na-
(
L-r) Lynn Usery and Charles C. Counselman III.
Awards & Scholarships
