Remote Sensing Ð this month's theme - has different definitions. In this issue are articles that describe both active and passive systems in which the sensor and the object are separated by air and/or space. Coming issues with themes such as 'Magnetometry and Gradiometry' and 'Underwater Imaging' will also devote attention to remote sensing techniques.

My first practical experience with the capabilities of remote sensing was back in the 1960s, taking part in a military oceanographic expedition near the Azores. We were being overflown at regular intervals by a participating aircraft measuring, among other things, sea-surface temperature. This was needed to calibrate and validate its sensor. The aircraft's crew tried to make us jealous by telling us that they were just a few hours away from being comfortably back on the ground - while we were riding out a storm which even managed to damage the barrel of our 40mm anti-aircraft gun. It was then that I learned how remote sensing enabled you to collect more data in a much more comfortable way.
Hydrographic data is not valuable only for the safety of navigation but can also give us a better understanding of our environment. Few technologies have made such a fundamental change to the collection of data as remote sensing. Up until fairly recent times observations were made while we happened to be there. Our knowledge and explanation of phenomena and models were based on these 'incidental observations'. Remote sensing gives us the possibility of 'continuous' observations, both at individual locations and over large areas, over longer periods of time. Volumes of data and our knowledge of oceans, coastal zones and weather have greatly increased thanks to the new remote sensing capabilities.
The better understanding of our environment and the data collected by the earth observation satellites (there are about 50 operational, with a 150 sensors looking at us) also gives us better weather forecasts. This, in turn, benefits our survey planning and offshore operations.

Remote sensing capabilities will greatly enhance the operational capacity of oceanographic and hydrographic ships. However, they might have a tendency to reduce numbers, for ships carrying such capabilities may be considered expensive to operate. The process of minimisation of ship's time may be countered by new questions raised by new methods of data collection. The SPOT and LIDAR described in articles in this issue are examples of technologies that may influence needed survey capacity (i.e. the number of seagoing surveyors). Another technology of interest for depth measurements is SAR (Synthetic Aperture Radar) which, by combining echosounder data with SAR images, can produce bathymetry data and thereby reduce surveying time.
All methods such as SPOT, LIDAR and SAR have limitations. But it is likely that in the future surveyors - as well as oceanographers - will find themselves spending more time ashore than in their present traditional environment: out at sea. Technicians may take over some of their former shipboard tasks but, do not worry, the surveyor's work is still there; it has only changed. Although even some calibration and validation tasks associated with satellite sensor data have been taken over by automated, ship-borne instruments (e.g. ocean colour and SST), surveyors will still be needed out at sea. And, lucky you, there's not much chance of a satellite trying to make you jealous with the taunt that 'he' will be out enjoying himself at a nice grounded bar that night.

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