An effort was undertaken to perform simple digital processing tasks using pre-existing general purpose digital computers. An experimental software package, LIGMALS, was obtained and modified for this purpose. The resulting software permits basic processing tasks to be performed including level slicing, gray mapping and ratio processing. The experience gained in this project indicates a possible direction which may be used by other developing countries to obtain digital processing capabilities

Nanayakkara, C.

Wagner, H.

English

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DIGITAL PROCESSING SYSTEM FOR DEVELOPING COUNTRIES
Chris Nanayakkara
Deputy Surveyor General of Sri Lanka
Colombo, Sri Lanka
Harvey Wagner
Environmental Research Institute of Michigan
Ann Arbor, Michigan
ABSTRACT
Digital data processing systems have, until
now, consisted either of expensive dedicated hard-
ware systems or complex software packages. An
effort was undertaken in Sri Lanka to perform
simple digital processing tasks using pre-existing
general purpose digital computers. An experimental
software package, LIGMALS, was obtained and modified
for this purpose. The resulting software permits
basic processing tasks to be performed including
level slicing, gray mapping and ratio processing.
The experience gained in this project indicates a
possible direction which may be used by other
developing countries to obtain digital processing
capabilities.
INTRODUCTION
As the field of remote sensing continues to advance, and major improvements
are made in analysis techniques, it is becoming increasingly obvious that
automated processing of digital data products is, for the most part, a necessary
component in a balanced program of remote sensing imagery interpretation and
utilization. When the user has available to him some of the expensive dedicated
hardware systems or complex analysis software that have been designed in recent
years, the processing of digital data products is a fairly straightforward task.
However, when no such hardware or software is available, and no major funding
can be obtained for the acquisition of these systems, the usual course of action
is to delete automated processing from the interpretation scheme. This is often
the case in developing countries. Very often when an attempt is made to develop
"home grown" processing systems using available computer components and local
scientists as the starting point, the lack of experience and the scarcity of
printed instructions on how to proceed in the development of such a system prove
an almost insurmountable stumbling block.
Such a problem was encountered in Sri Lanka, where a team from the Office of
the Surveyor General was attempting to implement digital processing techniques
for use with LANDSAT CCT's. This paper is a summary of the results of a project
undertaken jointly by Sri Lanka and ERIM which was funded, in part, under a
grant received from the U.S. Agency for International Development.
PROCEDURE
The major component of this project was to develop the capability of
Digital Processing of LANDSAT Data (on CCT) through computer facilities available
in Sri Lanka. Such available facilities were limited in computer capacity, to
48K of core memory. Other computer accessories were also limited to Card
Reader, Card Punch, Line-Printer, Mag Tape Drive and Disc Drive facilities.
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There were no facilities for interactive processing of data. We still do
not have this facility. Hence we had to resort to the batch-mode execution of
programs using a very small core memory capacity, available to the user.
This study commenced in the early part of May 1976. The computer facility
used by the Survey Department up to this period was the ICL 1901, 24K capacity
computer at the State Engineering Corporation. We had experience in executing
programs for Geodetic computations and Photogrammetric Aero-triangulation at
this facility. However, it was decided to conduct this investigation at the
computer facility of the State Department of Census and Statistics, especially
due to the great enthusiasm shown by the scientists there. Their computer
facility consisted of an IBM 360, model 25, computer with 48K capacity. In the
meantime, a study of the NASA publication "Generation and Physical Characteristics
of the LANDSAT 1 and 2 MSS Computer Compatible tapes", was being conducted. No
CCT was available at this stage. However, we wanted to obtain more information
regarding the problem of reading and preprocessing a LANDSAT CCT. Up to this
period a reference library on remote sensing was gradually developed. Reference
to this literature revealed that none of the publications contained any infor-
mation on such techniques. Though, all of them wrote at length on the signifi-
cant achievements and results of tests etc., there were no descriptions of the
actual techniques used. This was particularly lacking in the articles referring
to computer processing.
A working group was formed within the Survey Department, consisting of
personnel experienced in Photogrammetry, Scientific computer programming, Photo
Laboratory Techniques and Photo^interpretation. We then wrote to various
organizations and scientists involved in remote sensing and LANDSAT Digital
Data Processing, seeking information on this subject. The replies received were
not helpful. In fact, some expressed the opinion that LANDSAT CCT processing
would not be possible on such small scale, general purpose computers of the type
we have access to, in Sri Lanka. It was revealed that many organizations used
special purpose, high capacity computers or extremely expensive general purpose
computers of very high capacity with various display and inter-active capabilities.
The acquisition of such expensive hardware for our country could not be
justified by any stretch of imagination, considering the limited number of frames
required to cover the country, the limited frequency of coverage, the uncertainty
of regular coverage due to cloud-cover and tape recorder capacity limitations
on LAHDSAT and our own foreign exchange limitations.
A further expansion of the working group was necessary to investigate this
problem. Experts in computer systems analysis were co-opted into the group in a
consultative capacity. During this period, we were informed by ERIM of the
existance of an experimental digital processing package at the University of
Michigan for use with LANDSAT CCT's on small scale computers.. This processing
package was named LIGMALS (Landsat Interactive Gray Map and Level Slicing
system). Arrangements were made through ERIM to obtain a copy of this package.
We had the choice of only two LANDSAT frames which were suitable for
investigation purposes. The first was frame ID 1234-04233 of North-East Sri
Lanka acquired on 14 March 1973. The second was frame ID 2339-04151 of South-West
Sri Lanka acquired on 27 December 1975. The first frame covered an area which
has come under extensive development through the restoration of ancient irrigation
works supplemented with additional irrigation through the diversion of Sri Lanka's
largest river (Mahaweli) completed in January, 1976. The spatial distribution
of large homogeneous tracts of rice cultivation and the irrigation pattern was
clearly discernible in this LANDSAT image. But we were aware that from March 1973
onwards there were major changes in the development of this area mainaly due to
the diversion of the Mahaweli River. The use of this frame, 3 years after
acquisition, would have resulted in serious difficulties of correlating ground
truth with the LANDSAT data because we did not even have aerial photography of
this area taken around the same season. On the other hand the second frame was
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acquired in December 1975 and was somewhat more suitable for ground truth
correlation, through the use of aerial photography and short field visits from
Colombo. However, we were aware of the major problem of a very complicated
spatial distribution of the data within this frame. This area is highly developed
with homesteads mixed with coconut, rubber, small forest reserves and very narrow
and spatially complicated pattern of rice fields following the drainage pattern.
Due to lack of anything better, we were compelled to take up this frame for
digital processing. The CCT of this frame was received in July 1976.
We consulted local computer experts in the University, IBM and the Department
of Census and Statistics on how to access the data from the CCT. The consensus
of their opinion was that at some stage or the other, we had to go down to a
lower level language. Two persons were, therefore, sent for a two-month training
course in Assembler Language conducted by the Sri Lanka Branch of IBM. In the
meantime we received from ERIM, the LIGMALS software package. We started to de-
code and document this program and at the same time converting parts of this
program package to suit our local computer system as regards language and batch-
mode operation. With thisjpackage, combined with additional information [1,2] it
was possible to build up a viable program for batch-mode operation in our
system.
Due to the lack of visual display facilities the sections of the LIGMALS
program necessitating video display, were omitted or modified. The original
LIGMALS package was divided into five different stand alone programs for batch
mode operation. There are:
1) REFORM - a program to reformat LANDSAT CCT's into an IBM FORTRAN compatible
format.
2) RSET - a program to locate and extract a desired area to be processed
for further investigations.
3) ALSET - a program to automatically define level set boundaries for
use with the gray mapping routine.
4) PMAP - a program to generate a line printer gray map of an area utilizing
either automatically or manually derived gray-level boundaries.
5) RATIO - a program to apply a ratio processing algorithm to data to
obtain a new imagery channel of an area after performing
appropriate path radiance corrections.
Because the programs we received were optimized for use on the University
of Michigan computer system, which is a large time sharing system using multi-
processing and virtual memory techniques, some sections of the program had to be
extensively modified to be able to operate on the system in Sri Lanka.
Additionally, an Assembler language input routine had to be written to accommodate
EROS formatted CCT's which had been handled by system callable utility routines
in the University of Michigan system environment.
DISCUSSION AND CONCLUSIONS
The work performed in this study has shown that it is possible for a
developing country to obtain sufficient information to provide a starting point
for a digital processing capability. Further, once the basic LIGMALS capabilities
were implemented-in Sri Lanka, local scentists had obtained sufficient experience
with processing techniques to develop their own special purpose software without
additional help from outside of their country.
Based on the experience gained in the Sri Lankan study, ERIM has produced
LIGMALS/B which is a software system written totally in FORTRAN, and which is
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designed to function in a small to medium sized computer system environment.
Also, extensive diagnostic procedures have been developed for use when the
package is installed, a feature we believe is necessary since many times minor
problems may go unnoticed by scientists who are not yet used to the behavior of
digital image processing software. Further, compatibility with the large scale
LIGMALS system used at the University of Michigan at at ERIM is maintained so
that additional processing modules in use at these locations can be rapidly
incorporated for use when needed in developing countries.
Aside from the results obtained with the LIGMALS system, it has been shown
that effective low cost processing programs can be designed and implemented
in a developing country. This can be accomplished without requiring a major
commitment to specialized hardware systems or the use of major software packages
which require local scientists to go abroad to be trained in their use and
modification. It has also been found that technical assistance at the beginning
of such a development project will greatly speed the rate of progress in a
developing country.
It is hoped that the results presented in this paper will encourage other
individuals to attempt to expand their capabilities to include basic digital
processing of remote sensing data.
REFERENCES
1. Wagner, H.L., "Feasibility Study of an Interactive System for Processing
Digital Multispectral Scanner Data," 1976, Master of Science Thesis, School
of Natural Resources, University of Michigan.
2. Wagner, H.L., "An Interactive Digital Multispectral Data Processing Soft-
ware Package", 1976, Proceedings of the Fifth Annual Remote Sensing of
Earth Resources Conference, Tullahoma, Tennessee.
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