Symposium on Remote Sensing for Resources Development and Environmental Management / Enschede / August 1986
Selection of bands for a newly developed Multispectral Airborne
Reference-aided Calibrated Scanner (MARCS)
M. A. Mulders
Agricultural University Wageningen, Netherlands
K.Schurer
TFDL Wageningen, Netherlands
A.N.de Jong
TNO, Physics and Electronics Lab., The Hague, Netherlands
D.de Hoop
ITC, Enschede, Netherlands
SUMMARY: A 16 band scanner is constructed which contains besides an array of detectors for measurement of
radiation reflected and emitted from the land surface, the following:
- a reference sensor which measures the flux of radiation coming from above from sun and sky;
- a device for internal calibration of the signals derived from below of reflected and emitted radiation of
the land surface.
Further characteristics of the scanning device:
- Silicon, Germanium, Leadsulfide, Leadselenide and pyroelectric detectors;
- recording of data with videorecorders;
- total scan angle of 60 degrees;
- ground resolution at flying height of 500 m about 4.2 x 4.2 m .
A number of bands is selected for this scanner. The bands have a width between 50 nm and 150 nm in the 0.3-
3 pm range but become broader in the 3-10 pm range (width 700-1000 nm). An additional band is chosen around
10.5 pm with a width of 5000 nm. The choice of bands is directed by the possibilities in the 0.3-13 pm range
of the electromagnetic spectrum regarding information potential and transmission properties of the atmosphere.
Indications may be obtained a.o. about the presence of iron oxides, lime, gypsum, layer silicates, soil
moisture and about the coverage and condition of vegetation.
INTRODUCTION
Challenged by the high potential of multispectral
remote sensing techniques for inventory of arid and
semi-arid environments, the feasibility of a
multiband instrument for earth-observation from the
air was considered. As a result, a new airborne
scanning device is being developed by the Physics
and Electronics Laboratory T.N.O. (FEL-TNO, Den
Haag), ITC (International Institute for Aerospace
Survey and Earth Sciences, Enschede) and TFDL
(Technical and Physical Engineering Service,
Wageningen). The device should have a light weight
enabling its use in the field as well.
The original set of bands suggested by the first
author (AUW, Agricultural University, Wageningen)
covered the visible and near infrared. T.N.O.
proposed bands in the extension of these zones into
the ultraviolet and mid up to thermal infrared.
The scanner may be expected to be completed at
the end of 1986. The first test flights were made
in April 1986 with the aircraft of the ITC (PHITC
Piper Chieftain).
MARCS
MARCS is an acronym for Multispectral Airborne
Reference-aided Calibrated Scanner. The scanner
operates in 16 channels covering the range from
ultraviolet up to thermal infrared. It has an IFOV
of 0.5° x 0.5°, thus reaching a ground resolution
of 4.2 m x 4.2 m from an altitude of 500 m. The
scan width is 60°. In Fig. 1, a schematic
presentation is given of its design.
Use is made of a rotating mirror with a square
cross-section. Four scans are performed on each
full rotation of the mirror axis. In each scan 16
picture-lines are recorded simultaneously for each
of the bands. Thus, with an interval time between
scans of 1.2 s, a groundspeed of 56 m/s results in
a continuous recording of the scene under survey.
Choppers are placed in front of each array for
modulation of the incoming radiation flux and
clamping purposes.
Furthermore, internal calibration signals are
measured
in the dead
time
between
two scans.
By using interference
filters
and appropriate
detector
arrays, the
following wavelength bands are
taken for
measurement
:
band
centre
width
detectors
(nm)
(nm)
1
355
90
2
485
70
3
555
50
4
605
50
Si
5
655
50
6
800
100
7
870
60
8
1050
100
9
1640
80
Ge
10
1750
60
11
2175
150
PbS
12
2350
60
13
3750
700
PbSe
14
4850
700
15
9500
1000
pyro-electrical
16
10500
5000
material
For measurement of the incoming radiation, a
reference sensor is mounted on top of the aircraft.
This sensor uses the same bands as described for
the scanner and is developed by T.F.D.L. The
detectors have diffusing entrance windows to
closely approximate true cosine responses. Data are
recorded during the scan. They are merged into the
main data stream.
The very high amount of data requires specific
techniques for recording. For this purpose, T.N.O.
and ITC have developed a system using
videorecorders with digital data storage. For
analysis of the recorded data, ground systems
connected to large computers are available. By