Page 120 - Digital Analysis of Remotely Sensed Imagery

Storage of Remotely Sensed Data 91

FIGURE 3.5 A 36Gb, 10,000-RPM, IBM SCSI server hard disk, with its top
cover removed. Note the height of the drive and the 10 stacked platters (the
IBM Ultrastar 36ZX). (Copyright Hitachi.)

price for computer hard disks has tumbled (e.g., from over US $100 to
less than 1 cent per megabyte) over the last two decades, hard disks
(Fig. 3.5) are still more expensive than mobile storage devices per unit
data size. Thanks to these reductions in price, hard disks have become
a popular alternative media for data storage, especially for storing
raw remote sensing data, and intermediate results temporarily. There
are two types of computer hard disks in terms of their accessibility,
local and networked. The former resides at a single desktop computer.
Data in the hard disks are thus accessible to one image analyst at a
time. This is the preferred option only when one user is engaged in
analyzing the data. Networked hard disks reside in a server that
offers a high degree of flexibility in data accessibility. All authorized
users logged into the network have access to the data simultaneously,
if authorized. This data storage media is preferred if the data are
needed by multiple users working in a large research project or a
classroom setting, or they have to be accessed from different
terminals.

3.3 Format of Image Storage
A remote sensing image may be stored in one of many graphic
formats. Which format is the most appropriate depends upon the
image processing system being used. Each image analysis system
likely has its own proprietary format. Due to commercial sensitivity,
such image formats are not routinely disclosed to the public. Therefore,
these special image formats unique to a particular image processing
system (e.g., the IMG format in ERDAS Imagine) are beyond the