a, CA, 9-11 Nov. 1999 
ABI 
fes 
unser 
  
[PLES 
> Pembina river, a tributary 
| history of flooding in the 
the flood plain. An area of 
| by the STAR-3i system on 
Within this larger area, a 
icquired by EarthData on 
available to Intermap for 
re referenced to WGS-84 
88 geoid vertically. The 
t 5 meters while the laser 
eter  ArcGrid files. The 
d from the laser DEM by 
d was in the form of a bald 
| this and the following 
ng a commercial software 
m Northwood Geosciences, 
lient for doing comparative 
subset for this example is 
1 W°97° 27 °53") An 
M (Figure 3) shows the 
nes and the window within 
e located. 
eure 5 and Figure 6 are co- 
color table representations. 
laser DEM, the radar DEM 
radar minus laser) on a 3 
  
  
Bee 
& 
0 5 10 3 
pm, QUERN 
Kilometers 
  
  
  
  
Figure 3: Laser coverage area. Box outlines specific 
study area 
The laser DEM has had the vegetation removed while 
the radar has not. Therefore, the difference surface 
includes the vegetation which consists mainly of trees. 
The light brown colored areas are depicting maximum 
terrain excursions of about 2 meters. All vegetation, 
irrespective of height, is shown in green. 
Three rectangles show areas where local statistics were 
derived (refer to Table 2). Boxes A and C are in bald- 
earth areas. The mean and standard deviation of the 
individual DEMs describe the characteristics of the 
surface with noise and offsets superposed while that of 
the difference surface represents just the combined noise 
and offset differences inherent to the sources. If the 
majority of the noise is assumed to originate with the 
radar, then the standard deviation of the difference 
surface represents a 'noise floor' of about 30 cm for 
STAR-3i under these operating conditions. 
  
Kilometers ' 
  
Figure 4: Laser DEM (vegetation removed) — see 
text. Note boxes A, B, C for statistics samples 
Independently of this analysis, more than a thousand 
check points were measured using DGPS along roads in 
the larger area (more than 500 in the overlapping 200 
km? laser area) and provided to Intermap by TEC (the 
US Army Topographical Engineering Center) The 
mean difference (STAR-3i minus checkpoints) was 
about 10 cm over the laser overlap area with a standard 
deviation of 69 cm. This larger variation represents the 
addition of wider-area systematic errors superimposed 
upon the STAR-3i noise floor. 
It should be noted that the EarthData laser, at this time, 
was subject to a processing problem that caused a 
Systematic ripple and offset error to appear in the DEM. 
   
  
  
  
  
Kilometers ™ 
Figure 5: Radar DEM - all elevations greater than 
three meters above mean are colored green and 
represent vegetation 
  
  
  
  
Kilometers: aside? o e 
Figure 6: Difference Surface (Radar minus Laser) 
  
  
Cross-section Across Meander Scars 
  
251.0 Te c ceÓ—À 
250.5 - ERRORES SES 
250.0 
249.5 
249.0 
248.5 
Elevation (m) 
248.0 — STAR-3i Radar 
2475 — EarthData Laser 
247.0 = PT RU 
0 200 400 600 800 1000 
Distance (m) 
  
  
  
  
Figure 7: Elevation profile of radar and laser across 
meander scar features — see text. 
This is responsible for the mean differences observed in 
the two boxes and for the appearance of the color ripple 
aligned with the laser flight lines in Figure 6. The 
problem is apparently understood and currently being 
corrected (EarthData, Private Communication). 
The statistics for Box B are descriptive of the local 
canopy. The mean difference represents the mean