THE IMPACT OF OPTICAL STORAGE TECHNOLOGY ON 
REMOTE SENSING AND GEOGRAPHIC INFORMATION SYSTEMS 
W. Murray Strome 
PCI, 4800 Dufferin Street, Suite 202 
Downsview, Ontario, Canada M3H 5S8 
THE DATA STORAGE PROBLEM 
The launch of LANDSAT-1 in 1972 resulted in a sudden, 
tremendous growth in the amount of digital remotely sensed 
data. Ground stations were faced with the problem of recording 
50-100 digital LANDSAT scenes daily each containing about 25 
megabytes of data at a recording rate of 2 megabytes per 
second. 
At that time, standard computer peripherals included magnetic 
tape recorders with data densities of 200, 556 and 800 bytes 
per inch (50.8, 1412, and 2032 bytes/cm) with data transfer 
rates of up to 40 kilobytes per second and disk drives with 
data capacities of about 100 megabytes. Clearly, such 
equipment was incapable of handling the data volume provided by 
the satellite. The solution adopted by all groundstations was 
to use high performance analogue instrumentation recorders with 
special electronics to encode and decode the digital data. 
Typical recorders had 28 tracks recorded at a density of 10,000 
bits per inch (25,400 bits/cm) on each track. The tape speed 
used was 60 inches per second (152 cm/sec). Computer 
compatible tapes (CCTs) were produced for user distribution 
after the satellite pass by playing the data back through a 
computer at a reduced speed. In some installations, data were 
transferred to several CCT drives operating in parallel. A 
single scene could not be contained on a standard 1200 ft (366 
mu CCT, Thus, users would be supplied with up to 8 reels of 
tape (depending on the recording density) for a single scene. 
The LANDSAT-4 and 5 Thematic Mapper has provided an order of 
magnitude increase in data. Fortunately, magnetic recording 
technology has advanced considerably. A typical TM scene 
contains about 265 megabytes of data. Data are still recorded 
on specially modified multi-track analogue instrumentation 
recorders. However, the recording density is now typically 
30,000 bits/inch on each track (11,800 bits/cm/track) and tape 
speeds of up to 100 inches/second (250 cm/sec) are employed. 
Disk drives with capacities of 600 megabytes are in common 
usage and the CCT industry standard is now 6250 bytes/inch 
(2460 bytes/cm). However, even with this advance in 
technology, a full TM scene contains more data than can be 
recorded on a 6250 bpi CCT. Thus, a typical user product 
consists of one-quarter TM scene on a single 6250 bpi CCT or a 
full scene on four tapes. 
521