Honorary Managing Editor
“Remote sensing cannot replace man on ground, but can direct man’s efforts on ground to be more efficient.”
– Vikram Sarabhai
It was the concluding session of the First UN Conference on Peaceful Uses of Outer Space in Vienna. The year, 1969: Dr Sarabhai was summing up the report of the conference. The launch of ERTS, as Landsat was then called, was still three years away but the report identified an 18:1 benefit in using remote sensing for cartography and suggested the use of aerial sensors till such time as spaceborne sensors became available.
Forty years down the line, the promise of remote sensing has been realised substantially, if not in full measure. Sensor technology has progressed from complex electromechanical scanners and Return Beam Vidicon cameras used on Landsat to fully electronic charge coupled devicebased sensors, imaging radar and imaging laser systems. Spatial resolution has leapfrogged from 70 metres to submetre levels. It is interesting to note that the aerial camera is making a comeback in its digital avatar. Major aerial camera manufacturers are coming out with extremely sophisticated systems, which have rendered the traditional film cameras obsolete. Photogrammetrists, who tend to be extremely conservative, now accept the superiority of digital data for its better radiometric and geometric properties. However, the acceptability for space-borne data is still in question for scales larger than 1:45,000! Instrumentation for imagery interpretation and photogrammetry has drawn on the combined benefits of computational power and digital data from modern sensors to provide a breathtaking (and sometimes confusing) array of tools for the photogrammetrist. Digital photogrammetry and orthophoto generation is set to move into near real time operations, making the workflow from acquisition to data product nearly automatic. However, image classification techniques have fallen behind and there are few solutions for the very high-resolution multispectral imagery available from modern sensors.
There is no dearth of remote sensing satellites, both government sponsored and commercial, and this does move technology to higher and higher levels. However, on the access front, the cost of imagery often deters broad based usage, though efforts like Google Maps, Yahoo Maps and Microsoft Live Local, funded by advertisement revenue, have made impact in terms of popularisation of remote sensing. These services, together with GPS, provide location based applications, which have become popular but professional applications need data at a different level. However, in some cases government policy on high-resolution data is a hurdle. There is no universal policy. The USA sets a limit at 0.5 metres while India sets it at 10 metres. There are also questions as to whether data for public good should be free or at least subsidised.
The application trends are towards integrated use of remote sensing, GIS, photogrammetry and GPS. This calls for extra effort in the realm of standardisation and interoperability at various levels – data, software, hardware and applications.
All this is happening and more but in the ultimate analysis it is the local expert, the man in the field who plays a decisive role in how technology is brought to bear on immediate problems. That is what Dr Sarabhai pointed out – 40 years ago.