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Proceedings of Symposium on Remote Sensing and Photo Interpretation

(b) repetitive coverage at regular intervals (limited by cloud cover).
The ERTS-1 is equipped with two remote sensing systems: the return
beam vidicon cameras (RBV) and the multispectral scanner (MSS). However,
except for a short period in 1972 the RBV cameras have been switched off and
only the MSS images are available on repetitive basis. Though the capability
to monitor temporal changes on the earth surface over an extended period of
time is the ERTS strongest feature, there have been relatively few reports on
studies of multidate images. This was partly caused by difficulties to obtain
good quality images of test areas in required time intervals and partly by the
necessity to familiarize ourselves first with ERTS interpretation techniques
based on a single-date multispectral imagery.
ERTS images are available either in analog format printed on
black-and-white or color film, or in digital format printed on computer
compatible tapes. The latter were selected for our study for the following
(a) Analysis of seasonal changes requires multidate correlation of
several sets of ERTS multispectral images. This is very difficult
and slow by visual observation even when multispectral color viewers
are available.
(b) Digital images are not subjected to image degradation due to
photographic processing and reproduction. Once the ground data are
digitized on board of satellite there is no further degradation of
the digital image.
(c) Digital images printed on computer compatible tapes form direct
input into computerized image processing system.
This study had three main objectives:
(a) production of thematic map of the Larose Forest test area by
computerized processing of the ERTS single-date multispectral
digital images (Kalensky and Sayn-Wittgenstein, 1974);
(b) production of multidate thematic map of the same test area by
computerized processing of the ERTS multispectral digital images
recorded at three different dates;
(c) comparison of classification accuracies of the single-date and
multidate ERTS thematic maps.
The computer compatible tapes were recorded with density 800 bpi in
9 tracks. Two 2,400-foot tapes were needed for each ERTS scene. Selection of
ERTS scenes was based on the availability of tapes, quality of recorded
digital images and ease of their registration. The following three scenes
were selected for the single-date and multidate classification: