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TABLE 1.
International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Volume XXXIX-B4, 2012
XXII ISPRS Congress, 25 August — 01 September 2012, Melbourne, Australia
Check point accuracies derived from precise GPS points 1001:1015 and their corresponding ASTER
GDEMY2, OSGB and photogrammetrically derived heights (all heights with respect to the ODN vertical datum).
Pnt # Eastings Northings GPS ASTER | OSGB Photogramm.
height | height height height
1001 178689.5 832767.9 28 15 29 28
1002 178880.0 832864.3 22 10 23 22
1003 179457.5 832991.9 29 22 28 22
1004 178122.3 831466.6 26 18 24 26
1005 178448.0 831315.6 32 28 34 32
1006 177919.5 830051.4 96 91 99 96
1007 178461.6 830410.8 151 153 151 151
1008 180259.2 831473.0 95 102 99 114
1009 179626.8 830507.6 122 114 122 Na
1010 180518.2 832624.5 84 88 86 Na
1011 180440.1 830944.9 105 109 108 Na
1012 181591.5 833072.5 45 55 49 52
1013 182388.6 833039.8 52 54 52 52
1014 181457.2 831303.2 140 142 140 140
1015 182234.0 831316.3 144 153 145 143
RMS w.r.t. 7.3m 2.1m 3.7m
GPS height
4. RESULTS
The findings for Plockton are shown in Figures 1 and 2, for
Caerlaverock Merse in Figure 3 and for Wicken Fen in
Figure 4. The same methods are used in all three areas, that is
producing a difference map of the Aster and OSGB terrain
models - heights with respect to the same vertical datum
(ODN). Shifts from EGM96 to ODN are from the Google-
Earth-Plotter facility (Stillman, 2009). The legend for
differences between OSGB and ASTER is similar for each
test area and is in Fig 1a for the Plockton case.
Some consideration was given to the stack numbers also
supplied with ASTER GDEM v2. This gives, per pixel, the
number of images processed to provide heights. In the
Plockton case the maximum number was 7, which is low, and
the mean was 4; results are quoted as being especially poor
for stack numbers of 4 or less (Microlmages, 2009). The
correlation coefficient for stack number against absolute
height differences was only -0.07, indicating stack numbers’
unimportance in this case.
5. CONCLUSIONS
The ASTER GDEM v2 data are within their specified
accuracy of 17m and show no large negative bias; the
Wicken Fen area shows a small positive bias. Perhaps the
bias previously found related to the choice of datum? Largest
discrepancies are found where slopes are steep and in coastal,
low lying areas where image matching may be difficult. An
anomalous situation (level arable land below sea-level)
requires further consideration, particularly considering
ASTER GDEM's potential use for flood management in
these and coastal areas.
6. REFERENCES
Lemoine, FG., Kenyon, SC., Factor, JK., Trimmer, RG.,
Pavlis, NK., Chinn,DS., Cox, CM., Klosko, SM., Luthcke,
SB., Torrence, MH., Wang, YM., Williamson, RG.,
Pavlis, EC., Rapp, RH. and Olson, Tr., 1998. “The
Developoment of the Joint NASA GSFC and NIMA
Geopotential Model EGM96",
http://cddis.nasa.gov/926/egm96/ egm96.html
Li, P., Li, Z., Shi, C., Muller, J-P., Drummond, J., and
Liu, J., 2012. “Validation of ASTER GDEM Using GPS
Benchmarks and SRTM over China", Int.Jo.RS, in press.
Stillman, D.M., 2009. “Plotting Surveying Data in Google
Earth", http//code.google.com/ p/google-earth-plotter
Microlmages Inc, 2009. “ASTER GDEM Accuracy
Assessment" http://www.microimages.com/documentation/
TechGuides/75asterDEM.pdf
7. ACKNOWLEDGEMENTS
Anne Dunlop, Kenny Roberts and the BSc Class of 2007
Geolnfo&MappingScience students, Glasgow Univ., for GPS
observations.
(i) Crown Copyright/DatabaseRight 2012. An Ordnance
Survey/EDINA supplied service.
