A new initiative at The University of Calgary is 
the VISAT program which combines a GPS 
receiver, a strapdown INS, and a cluster of CCD 
cameras mounted in a van. Requirements for the 
system are to provide precise positions at the 0.3 m 
level (RMS) of the cluster of CCD cameras. The 
digital imagery is then used to acquire positions of 
objects in the road corridor within a 50 m radius. 
These points are required with a 0.1 m relative 
accuracy. Tests have been conducted to confirm that 
the system can deliver these levels of accuracy, 
and further details are given in Schwarz et al. 
(1993). Another system which has been developed 
at Ohio State University is described in Bossler 
and Novak (1993). 
5. MARINE APPLICATIONS 
5.1 Water Level Profiling 
Precise knowledge of water levels is essential for 
tidal studies and other hydrographic purposes 
such as the establishment of chart datums. GPS 
offers the possibility of determining water level 
profiles with a cm-level accuracy using carrier 
phase measurements on-the-fly. Accurate Bench 
Marks (B.M.'s) can also be established along the 
shores if an accurate geoid model is available. 
This is an important development since levelling 
operations may be prohibitive in remote areas such 
as the McKenzie River in Northern Canada. A 
feasibility study was conducted by The University 
of Calgary in conjunction with the Canadian 
Hydrographic Service (CHS) to obtain water level 
profiles and establish B.M.'s along an 80 km 
segment of the Fraser River, British Columbia. A 
first order levelling line along the river was used 
to assess the accuracy of the GPS-derived 
orthometric heights. 
Results from the test are given in Lachapelle et al. 
(1993) and show that an accuracy of about 5.5 cm 
(RMS) could be achieved between the GPS-derived 
orthometric heights and the levelled B.M. height. 
Part of the error budget is due to the height 
transfer method (accurate to about 2 cm) as well as 
the geoid. Overall, the feasibility study was 
successful and the GPS-derived water level 
profiles are being analysed to determine the extent 
of tidal and other effects. 
5.2 Attitude Determination 
The use of attitude determination systems in the 
marine environment is important for the correction 
of hydrographic data from multi-beam acoustic 
170 
surveying, for example. Traditionally, INS have 
been used since no other system has shown the 
capability of providing the level of required 
accuracy. However, INS drift over time so a cost- 
effective alternative is a GPS attitude 
determination system. These systems can either be 
self-contained units which is one receiver with 
several channels dedicated to each antenna 
(usually up to four), or may be comprised of several 
independent receiver systems. 
The latter case was tested in June, 1993 in a joint 
effort between The University of Calgary and 
CHS. Four NovAtel GPSCard™ receivers were 
mounted on a hydrographic survey vessel with 
separations of 12 to 42 metres. Data was collected 
at a 10 Hz rate and post-processed to derive the 
ship's roll, pitch and azimuth. In the test, the 
ship's roll reached up to 10 degrees and when the 
GPS results were compared to the roll derived from 
an onboard INS, the RMS agreement was at the 
level of 2.7 arcminutes, with an agreement of 1.1 
arcminutes during straight portions of the 
trajectory. Sample roll results are given in Figure 7. 
These results clearly show the feasibility of using 
multi-antenna GPS for accurate attitude 
determination. It is expected that these systems 
will be further utilized in the marine environment 
with the continual decrease in GPS receiver costs. 
See Lachapelle et al. (1994) for more information 
on the above test. 
0.4 
  
Mean = 0.0036 deg 
RMS - 0.045 deg 
c 
N 
1 
-0.24 
Roll Differences (deg) 
e 
1 
0.4 
  
  
  
UTC (seconds of the day) 
Fig.7: GPS-INS Roll Differences - June 93 Test 
6. AIRBORNE APPLICATIONS 
Many of the current airborne GPS applications 
centre around the photogrammetric and remote 
sensing areas as well as for precision landing of 
civilian aircraft. The latter application will not 
be discussed in this paper, but can be found in 
existing literature. 
43000 44000 45000 46000 47000 4800 
  
The Unive 
the develo 
precise 
determina 
eliminatic 
applicatior 
system are 
use as we 
the require 
for large-: 
relaxed to 
applicatio 
sufficientl 
where the 
arcsecond: 
GPS/INS 
found in S« 
Several fl 
confirm th 
for precis 
difficulties 
during suc 
required. 
photogram 
determine 
which ther 
coordinate 
build redu 
ground G 
trajectorie: 
described 
when four 
and two o 
over 100 kr 
10-20 cm le 
measureme 
= 
Fig.8: 
Many ott 
environme 
positioning 
This work 
University 
in their m 
1994). The 
tests have