Symposium on Remote Sensing for Resources Development and Environmental Management/Enschede/August 1986 
© 1987 Balkema, Rotterdam. ISBN 90 6191 674 7 
1063 
Working Group 6: Hydrology 
K.A.Ulbricht 
Chairman 
R. Spanhoff 
Liaison 
The activities of Working Group VI during the 
Enschede ISPRS conference 1986 involved one main 
session with 2 speakers, two oral sessions with in 
total 7 speakers planned, two poster sessions with 
in total 19 presentations, and one discussion meet 
ing. All but 5 presentations were given: the authors 
of two (posters) contributions did not show up unex 
pectedly, for the other three (one oral and two pos 
ter presentations) it was known or anticipated. 
The number of people attending the oral sessions 
was about twenty on the average, and slightly over 
fifty during the invited talk. The above figures 
illustrate the success of our meeting. The only dis 
appointment was the small number of participants in 
the discussion meeting. 
The total field of Working Group VI is very broad, 
covering all aggregation phases of water, from snow 
and ice, surface- and groundwater till water vapour; 
the latter, e.g., as a term in atmospheric correc 
tion procedures. So, apart from the general overview 
in the invited talk, the presented 23 papers, which 
in themselves ranged from a purely theoretical to a 
highly observational nature, can merely touch some 
aspects of some subjects for which recently progress 
has been made. Nevertheless, some general remarks 
and conclusions can be extracted. 
1. Relatively much attention was paid in the oral 
presentations to more basic work aiming at a math 
ematical-physical description of the phenomena of 
interest: of the seven papers, one dealt with a 
mathematical description of the atmospheric correc 
tion based on one parameter, which can easily be 
obtained experimentally; one paper gave a model des 
cription for water-depth and bottom-composition as 
sessment; and one presented laboratory experiments 
which provided a better description of the wave 
length dependence of the light absorption by aquatic 
humus, and its possible consequences for the bottom- 
depth and water-component retrieval procedures. 
1.1 Conclusion 
We feel that this basic approach of remote sensing 
in the field of Working Group VI was appropriately 
highlighted, since it is imperative that theory and 
experiment intermingle as equal partners in order to 
make progress in this area. 
2. Being active in remote sensing is nowadays, 
rightly so, more and more considered from a user’s 
starting point. That is, remote sensing methods are 
invoked as one out of more, often complementary, 
measuring techniques to answer existing questions. 
This observation was stressed explicitly in the in 
vited talk by Prof. Cracknell, who quoted our state 
ment on this point of the programme of the confer 
ence prepared for the members of Working Group VI: 
"Remote sensing is no more but certainly no less 
than a (class of) measuring technique(s) employed to 
gather data on an object. Major differences with 
’standard’ in-situ techniques is the synoptic view 
over vast areas like oceans. This often renders qual 
itative data worthwhile but, of course, quantitative 
information has to be preferred. However, measuring 
is not a goal in itself. A remote sensing technique 
is borne out only then, when it is invoked to solve 
existing (in this case oceanographic) problems; in 
such a case it will be readily applied as one out of 
a series of measuring techniques, the others being 
either in-situ measurements or other remote sensing 
techniques". 
It is noteworthy in this respect that professor 
Cracknell postulated that, e.g., oceanographic 
cruises will always be necessary in addition to remo 
te sensors. 
A nice illustration of this ’user-approach’ was 
presented in the co-invited talk given by Dr. Jons- 
son. Setting up a current model for the Strait of 
Oresund, he has looked for remote sensing data which 
could help herein. A nice feature was, furthermore, 
that qualitative remote sensing data could be used, 
in a kind of sensitivity analysis, to see which 
(sometimes unexpected) effects should be included in 
the model, and which terms could be neglected. Simi 
lar trends were observed in some other presentations 
as well. 
2.1 Recommendation 
This ’user-approach’ in the application of remote 
sensing techniques should be pursued. 
3. The future of Working Group VI of Commission VII 
of the ISPRS was discussed in a dedicated session in 
which only eight persons participated. This meeting 
and its conclusions can, therefore, not be considered 
as representative for the Working Group. The feeling 
was that the Working Group should continue to act as 
a forum to exchange information not only about re 
sults, but also about who is doing what and, poss 
ibly, with whom one can exchange which data. No need 
emerged from joint projects to be executed by the 
Working Group.