investigations about the performance of fast OTF ambiguity 
solutions with the prime objective to look into the operational 
reliability of the method as function of the base length, i.e. of the 
distance between stationary receiver(s) and mission area. A working 
group was established under the chairmanship of Prof. O. Anderson 
(Agricultural University, As, Norway) and the author. Two pilot 
centres in Às (Department of Mapping Science, Agricultural 
University) and Stuttgart (Institute of Photogrammetry, University 
of Stuttgart) were charged with the execution of the investigations. 
The experimental tests make use of two photogrammetric testfields: 
(1) Testfield Fredrikstad near As, extension 4.5 km x 6.0 km, 
52 known signalized points. 
(2) Testfield Vaihingen/Enz near Stuttgart, extension 4.7 km 
x 7.3 km, 40 known signalized points. 
The set up of the tests was simple, in principle. Flight lines with 
continuous GPS recordings (C/A code and L1/L2 phase 
observations) were to go repeatedly over a testfield. When flying over 
the testfield the air survey camera would take photographs, whilst 
outside the testfield only the GPS recordings would continue. The 
crew was not to take the risk of signal interruptions into special 
consideration, i.e. fly normally, or even go intentionally into steep 
turns, in order to provoke signal loss of lock, for the purpose of the 
investigation. The flight duration, i.e. the total trajectory, should 
cover at least 1.5 hours. During the flight simultaneous GPS data 
recordings were to be taken at several ground receiver stations, at 
different distances from the mission area. It was expected to get 
several testflights, possibly with different airplanes and different GPS 
receivers. 
For the GPS data processing, including OTF ambiguity solutions, in 
first instance commonly available software in form of different 
software packages was to be applied, as different programs may have 
different performance. 
The first part of the investigations was designed to evaluate and 
compare the restored GPS flight trajectories resp. the OTF ambiguity 
solutions in relation to the different ground receiver stations. In the 
second part the GPS results would then be evaluated in absolute 
terms, by comparing the GPS positions at the camera air stations 
with the actual perspective photo centres, as derived by conventional 
aerial triangulation of the images taken over the test areas. Thus, the 
controlled parts can only refer to sub-intervals of the continuous GPS 
trajectories. 
There are four completed flight missions of summer and fall 1995 
which are used for the present investigations (some additional data 
sets may be considered at a later date): 
(1) mission of 26 July by Hansa Luftbild GmbH, Trimble 4000 
SSE receiver, testfield Vaihingen, 6 GPS ground stations, 
distance up to 386 km, photo-scale 1 : 13000, 
(2) mission of 9 October by Schweizerisches Bundesamt fiir 
Landestopographie, Trimble 4000 SSE receiver, testfield 
Vaihingen, 7 GPS ground stations, distance up to 386 km, 
photo-scale 1 : 15000, 
(3) mission of 11 October by Norsk Luftfoto og Fjernmaling 
A/S, Ashtech Z 12 receiver, testfield Fredrikstad, 9 (+11) 
GPS ground stations, distance up to 110 km (2200 km), 
photo-scale 1 : 5000, 
(4) mission of 13 October by Fotonor A/S, Trimble 4000 SSE 
receiver, testfield Fredrikstad, 9 (+11) GPS ground stations, 
distance up to 110 km (2200 km), photo-scale 1 : 5000. 
The locations of the GPS ground receiver stations of missions (1) 
and (2) are sketched in Fig. 1. 
2 
  
  
  
  
  
  
Figure 1: Location of testfield Vaihingen with 
GPS ground stations 
1.4 Test flight Vaihingen by Hansa Luftbild 
The photogrammetric and the GPS data processing of the various 
data sets has started, at both pilot centres As and Stuttgart. The 
investigations being in execution it is too early to submit a final 
report. In this paper the preliminary results of the mission (1) of 26 
July 1995 by Hansa Luftbild of the Vaihingen test area are 
presented, as processed with the standard Trimble software package 
GPSurvey 2.0 (by M. Cramer and M. Englich of the Stuttgart pilot 
centre). 
Fig. 2 and 3 display the flight lines and the photo strips of that 
mission which extended over 2 h 12 min (1 h 21 min in the test 
area). The test block has multiple photo coverage, consisting of 2 
photo-blocks of 3 strips each (flown in both directions) and 1 photo- 
block of 5 cross-strips, each of the 3 photo-blocks having 60 % side 
overlap. The wide-angle aerial photographs were taken with a Zeiss 
RMK TOP camera at 2000 m flying height (photo scale 1 : 13000). 
The airplane (Cessna 404) had 3 GPS antennae mounted, of which 
2 were connected to Trimble 4000 SSE receivers. There were 5 GPS 
ground receiver stations operating during the flight mission, namely 
stations A (in the test area), S (at Stuttgart University), D (TH 
Darmstadt), F (IfAG Frankfurt), H (Hannover). The distances to the 
testfield are, respectively, 0, 22, 106, 130, and 386 km. Station D 
recorded with a Trimble SSI, all other stations with Trimble 4000 
SSE receivers, the last station (H) being a permanent station. 
Altogether, there are 5 independent GPS data sets for either antenna 
on the airplane. 
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B6. Vienna 1996 
  
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