Since the beginning of the
space age, a remarkable progress has been made in utilising
remote sensing data to describe, study, monitor and model the
earth’s surface and interior. Improvements in sensor
technology, especially in the spatial, spectral, radiometric
and temporal resolution, have enabled the scientific community
to operationalise the methodology. The trend of development of
remote sensing is being from panchromatic,
multi-spectral, hyper-spectral to ultra-spectral with
the increase in spectral resolution. On the other hand,
spatial resolution is reaching its highest side of one metre
resolution. The operational remote sensing satellites LANDSAT,
Indian Remote Sensing Satellites (IRS series of satellites),
IKONOS etc. are providing earth data in different improved
spatial and spectral resolutions. The value added products
such as Orthophotos, standard DEMs, DEMs with specified level
of details, geocoded images, fused images are providing the
user community a big support.
Future Indian Remote Sensing SatellitesThe
futuristic scenario of the Indian Remote Sensing Satellite programme
includes Technology Experiment Satellite (TES), RESOURCESAT (IRS P6),
CARTOSAT (IRS P5) and OCEANSAT (IRS P7) satellites.
TES
Mission will be launched in July 2000 having PAN sensor with 2.5
metres resolution with high temporal resolution. This satellite is
launched to provide hands on experience in complex mission operations like
step and stare manoeuvres and onboard earth rotation compensation
etc.
Resourcesat (IRS P6) will have three sensors, LISS-3, LISS-4
and Advanced WiFS (AWiFS). This satellite will provide an enhanced
multispectral/ spatial coverage. AWiFS has a greatly improved spatial
resolution of 70 metres resolution with repetivity of five
days.
Cartosat (IRS P5) is scheduled to be launched in March 2002
to generate orthoimage, DEMs, and to generate high precision
georeferencing for cartographic mapping.
Oceansat (IRS P7) is
scheduled for launch in year 2003. The applications shall include
measurements of sea surface temperature, chlorophyll pigments and sea
surface wind direction and speed.
High Resolution Satellite Data
Viewed from the point of view of information content, higher
spatial resolution permits the discrimination of smaller units of material
on the earth’s surface. At present, the civilian systems having high
spatial resolution are the panchromatic data from IRS-1C and IKONOS
satellites having 5 metres and one metre resolution
respectively.
IKONOS satellite also has 4 metre
multispectral data. Similar satellites from ORBIMAGE and
EarthWatch Inc. are planned for launch this year. The
prohibitive cost of commercial satellites is a major hindrance
in their widespread use.
New high resolution satellites are also planned. The
European Space Agency (ESA) has scheduled next year launch of the biggest
EO satellite to date. ENVISAT-1 will have improved technical
characteristics compared to its predecessors (ERS-1 and 2 with advanced
synthetic aperture radar). The operating characteristics of these new high
resolution sensors are summarised in Table 1.
Wide Field Sensors
for regional scale mappingWiFS data of IRS 1C/1D provides the
advantage of covering a very large area in a single instantaneous field of
view (IFOV), avoiding any illumination difference. Suitability of such
moderate resolution data for regional vegetation as compared to AVHRR
data marks better choice for monitoring and research. The pixel size
of 188 metres suits regional scale mapping.
WiFS data enables rapid change assessment and early warning in
certain episodic events like forest fire, drought etc. Its high temporal
resolution i.e. five days and large area coverage (810x810 sq kms) is
helpful in developing improved yield models and assessing crop
condition.
Digital Elevation ModelsAcquiring highly
detailed elevation data always has been a complicated business.
Although GPS technology and digital photogrammetry have improved the
process, there is still a considerable amount of effort and time involved.
Recent developments of light detection and ranging (LIDAR) and
laser terrain mapping systems, however, may dramatically reduce the time
and efforts needed. With current systems, it is possible to survey by air
thousands of square kilometres in less than 12 hours and have a highly
detailed digital terrain model available within 24 hours, with vertical
accuracy of 15 centimetres and an elevation relative accuracy of about 5
centimetres.
IRS 1C and IRS 1D satellites are also providing the
stereo pair of images for use in generation of the DEM.
The costs of generating DEM vs.
level of detail are given in the following figure. Where :
- : Aerial Photography (tropical)
- : Aerial Photography (Urban)
- : STAR 3I, Interferometric Radar
- : Airborne Laser Scanner
- : STAR 3I, Global Terrain
- : IRS/Spot Satellite
- : Satellite Stereo (RADARSAT)
- : ‘Global Terrain’