3 - THE SEDIMENT STUDY 
3.1 Field data 
The field experiment on the Plaat van Walsoorden took place on 7 September 1993, at least a clear wty in 
the region of the test site and also a day of Landsat 5 passage (track 199, scene 24). From 11.00 AM untill 
15.00 PM spectral measurements of 23 sediment samples were collected. On each sample location 5 
reflectance measurements were averaged to give a spectral reflectance signature of that particular sample. 
All samples were analyzed to give grain size composition as well. 
3.1.1 Grain size distributions On the Plaat van Walsoorden from the top 5 cm of the sediment 23 samples 
were taken, which were subsequently analysed using a standard technique developed by GeoSea Consulting 
on a Malvern 2600 L laser particle size analyser. This instrument measures the diffraction pattern caused by 
sediment particles, suspended in water, being continually passed throug a laser beam. It uses lenses of 
different focal lengths to measure the concentration of particles. Three distributions are measured at each 
sample and the results averaged. Besides a size distribution also percentages of gravel (>.25mm), sand 
(0.063-0.25 mm), silt (0.02-0.063 mm) and clay (<0.02 mm) in each sample have been calculated and 
reported. None of the samples in this experiment contained any gravel. Knowledge of the mud fraction (=silt 
+ clay -> grainsize <0.063 mm) because of the fact that mainly the fine sediment fraction is the carrier of 
contaminants. 
3.1.2 PSII measurements Reflectance spectra of all sediment samples were measured with the PS1I 
fieldspectrometer. These were obtained by repetitive scanning of the target (the sediment surface) and a 
Lambertian reflecting reference panel. The reflectance in channel i of PS II is then calculated by ratioing the 
two measurements according to: 
R, = Rp, • DN u / DN p , (1) 
with: R, 
Rp 
DN„ 
DN pl 
: reflectance in channel i 
: Lambertian reflectance factor of the reference panel 
: measured digital numbers from the target in band i 
: measured digital numbers from the reference panel in band i 
3.2 Airborne data 
Table 1. casi bandsettings for the sediment 
study. 
casi SETTINGS 20/9/93 
BAND 
WAVELENGTH 
BANDWIDTH 
1 
420 
80 
2 
485 
50 
3 
525 
30 
4 
555 
30 
5 
585 
30 
6 
610 
20 
7 
630 
20 
8 
650 
20 
9 
680 
40 
10 
720 
40 
11 
760 
40 
12 
815 
70 
In our experiment the casi was flown at an altitu 
de of 10,000 ft in spectral mode with a number of 
12 bands programmed, resulting in pixels of appr. 
4x4 m 2 . The casi bandsettings for the experiment 
were chosen as follows: 12 contiguous bands, 
ranging from 380 to 840 nm (see table 1). This 
definition of bands turned out to be a good com 
promise between the optimal definitions for both 
the sediment and the vegetation study. The spec 
tra can be well characterized using those bands. 
Simulation of the first four bands of Landsat TM 
is also possible. The data were acquired while 
flying in a twin engine Piper Navajo Chieftain 
and sensor attitude and position were measured 
with a vertical gyroscope and a Global Positio 
ning System (GPS). Roll, pitch and differential 
GPS data were collected. Even with the absence 
of a heading sensor the overall geocorrection is 
good when using dedicated software (Cosandier et 
al„ 1992). The final conversion to UTM was 
performed using ground control points and stan 
dard software.