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3 SUBSEQUENT DEVELOPMENTS 
The second edition of the Manual was published in 
1983. Inevitably there must have been a significant 
lapse of time between the final revision of copy and 
the actual appearance in print - especially of such 
a large book as the Manual. Perusal of the references 
shows that the relevant chapters include coverage of 
work published up till about 1981. Perhaps the most 
significant thing which has found its way into the 
literature since then is the vast amount of oceano 
graphic work which has been carried out using the 
SEASAT data set. 
SEASAT was launched as a "proof-of-concept" oceano 
graphic applications satellite. It only generated 
data for about three months following its launch in 
1979 but it was several years before substantial 
inroads were made into the processing and inter 
pretation of the data set. Optical and infrared 
scanners had been flown on many satellites before 
the launch of SEASAT and although there was an 
optical and infrared scanner on SEASAT it was of 
relatively minor importance; it only had two spectral 
bands and the spatial resolution was very poor (2 km 
in the visible band and 4 km in the thermal infrared 
band). The importance of SEASAT lay in the extensive 
suite of active and passive microwave sensors flown 
on it; these included an altimeter, a scatterometer 
and a synthetic aperture radar (SAR) which are active 
instruments and the scanning multichannel microwave 
radiometer (SMMR) which is a passive instrument. 
None of these microwave instruments was completely 
new and untried and most of them had been flown on 
previous satellites. However, what was new was (a) 
the flight of a synthetic aperture radar in space, 
(b) the collection of so many microwave instruments 
on one satellite and (c) the significant amount of 
simultaneous in-situ data collected during the very 
short useful lifetime of the satellite. Essentially 
the information obtained from the non-imaging active 
microwave instruments, that is the altimeter and the 
scatterometer, is related to the shape of the surface 
of the water, whether the mean surface (the geoid) or 
disturbances on the surface (wave motions and, 
therefore, wind speeds and wind directions). The 
SMMR can be used to give information about sea 
surface temperatures as well as about sea surface 
stateAvindspeed. While these three instruments are 
non-imaging instruments, the synthetic aperture radar 
is an imaging instrument which, after substantial 
processing of the data, produces images of the sea 
surface. The most obvious feature of the image is 
surface wave patterns but other features have also 
been observed in some of the data; these other 
features include internal waves and, in favourable 
circumstances, manifestations at the bottom topo 
graphy . 
In some ways SEASAT was enormously successful. It 
convinced the oceanographic community of the 
importance and potential of microwave remote sensing 
techniques. At the same time it was very 
frustrating because, at the time, the data handling, 
processing and interpretation techniques on the 
ground were not properly geared up to handling the 
quantity of data generated. It was also frustrating 
in the sense that there was no immediate successor 
and the oceanographic community is having to wait for 
about a decade after SEASAT before oceanographic 
microwave remote sensing instruments will again be 
flown in space (on ERS-1, MOS, NOSS, etc.). An 
extensive account of work based on SEASAT will be 
found in the book edited by T.D. Allan (1983). 
The second thing that should be mentioned to 
supplement what is described in the Manual is ground- 
based radars. This is not to suggest that the 
importance of ground-based radars had not been 
appreciated before about 1980/1981. A ground-based 
radar may be used to observe the sea surface 
directly or by reflection at the ionosphere. Such a 
system gives information, very similar to that 
obtained from a synthetic aperture radar (SAR) flown 
on a satellite, about the state of the sea surface 
and thence about currents and near-surface winds. 
The most important difference is that the range of a 
ground-based radar is quite small so that only a 
relatively small area of sea surface in the vicinity 
of the ground-based radar can be studied. With a 
satellite, however, it is possible, in principle at 
least, to obtain data for any part of the sea any 
where on the surface of the Earth. The capital and 
running costs for a satellite are, however, enormous 
compared with the quite modest costs of a ground- 
based radar system. Some recent accounts of ground- 
based radars have been given by Shearman (1981) and 
Wyatt (1982). 
A third area in which significant developments have 
been made since 1980/1981 is in airborne lidar for 
bathymetric work. There is only about one page 
devoted to this subject in chapter 28 of the Manual. 
The last few years have seen considerable advances. 
Originally only profiling systems were available but 
recently scanning systems have been developed and 
evaluated in the field. A comprehensive review is 
given by Muirhead and Cracknell (1986). 
4.PRESENT POSITION AND FUTURE DEVELOPMENTS 
The present position and future developments should, 
perhaps, be considered from the point of view of (i) 
(deep sea) oceanography, (ii) estuaries and coastal 
regions and (iii) hydrology. 
4.1 Oceanography 
As far as oceanography is concerned, present routine 
data from satellites is confined to the optical and 
infrared parts of the electromagnetic spectrum. 
The principles, and importance of the applications 
of optical and infrared scanner data to oceanographic 
problems are widely accepted by oceanographers 
although, not surprisingly, there are a number of 
details that are still actively being pursued in the 
research mode. The supply of data is good; in my 
experience at least it is not so much a shortage of 
remote sensing data but delays in the distribution 
system and a lack of resources for the processing and 
interpretation of the data that constitute the main 
difficulties. What we need to try to achieve in 
the next few years is a streamlining in two senses. 
The first concerns the distribution of data. In some 
work there is a need for very near to real time access 
to the data, perhaps in the form of an image or 
perhaps as full digital data; with modern developments 
in communications systems it should be possible to 
achieve this. The second concerns the software for 
processing the data. Many of us have software that 
has been developed in an ad hoc manner and is not 
only untidy and not properly documented but is also 
difficult and inconvenient to use. Streamlining of 
the software is not intrinsically difficult but it 
requires time and effort, which have to be financed. 
Probably one of the most serious outstanding problems 
is that of making atmospheric corrections to the 
satellite scanner data. With infrared scanners the 
prospects are good and corrections can be made either 
using the multichannel approach of the existing 
AVHRR/2 (the second version of the Advanced Very 
High Resolution Radiometer) or using the two-look 
approach of the ATSR (Along Track Scanning Radio 
meter) which is currently being developed to be 
flown on ERS-1 in a few years time. With optical 
scanners the prospects are not so good, at least in 
the short term. The atmospheric contribution to the 
satellite-received radiance at optical wavelengths 
constitutes a considerably greater percentage of the 
total signal than it does at thermal infrared wave 
lengths. Existing scanners only have a very small 
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