Remote sensing images of the ocean surface have a great potential for allowing monitoring of ocean dynamics. This chapter reports and compares in-water thermal structure data from three instruments-a long thermistor chain, a short thermistor spar, and an acoustic doppler current profiler-with data from a near-coincident infrared (AVHRR) image. The comparison underlines our need for a detailed knowledge of deep structures and of their interaction with the surface before remote sensing images can be used reliably to enhance what is a generally inadequate provision of in-water data.

THE IMPACT OF MODERN OBSERVING TECHNIQUES ON OCEANOGRAPHY

The major impact of technology on oceanography over the past twenty years has mainly been through advances in electronics, particularly in the electronics of physical measurement and data storage. Although this trend will no doubt continue, it is apparent that space technology is already having an increasing impact through its growing ability to provide detailed synoptic measurements from large areas of ocean surface The combination of these two trends will allow major advances in our understanding of the oceans, when the space measurements are adequately supported by detailed in-water measurements.

Although this possibility has been recognized for some time now, examples of direct comparison of coincident data, provided at comparable sampling scales by in-water and remote sensing techniques, have been relatively few This chapter describes some recent results in which this comparison has been made.

Although satellites, and other orbiting space platforms such as space stations, can also measure sea surface elevation and surface waves along relatively narrow tracks, this chapter rather considers the possibilities offered by space-borne sensors which give large-area images. Passive infrared systems are considered here, but the conclusions drawn can be expected to apply more generally, across the whole range of future remote sensing possibilities.

This chapter also draws on data obtained with two in-water techniques that have been developed quite recently thermistor arrays and the acoustic doppler current profiler These techniques exemplify the Impact of modern electronic technology on the subject.

Fig 1 An infrared AVHRR image of the Iceland - Faeroes region obtained on June 21, 1986, at 1334Z. The warmer water appears darker in this image. The contrast has been stretched to give a good indication of the horizontal variability in the region.(available in full paper)

SATELLITE INFRARED IMAGES

High-quality images of the earth are provided routinely by the NOAA-TIROS series of satellites, carrying the advanced very high resolution radiometer (AVHRR) sensor at an altitude of 840 km. Detecting radiation m the visible and near infrared, this sensor package can give 1 km resolution images of ocean surface thermal radiation. Such images are Invaluable sources of information about the spatial position and extent of ocean features that Involve water masses of different temperature, ocean fronts being a good example.

Ideally, such images should allow us to make detailed synoptic extrapolations of necessarily sparse and spatially limited in-water data, with the aim of completely specifying the water mass structure of very large regions.

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