International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B7. Istanbul 2004
with ground station data - “ground truth” - in order to provide
calibrated data sets.
The cost of collecting and using remotely sensed data could be
very high, so the use of this data should be carefully evaluated.
The cost of collecting adequate ground-station data could be
even higher, so the trade-offs between the two data types need
to be examined.
2. THE HYDROLOGICAL REMOTE SENSING
SYSTEM
A remote sensing system for the surveillance and management
of water resources can be defined as the result of the co-
ordination use of the knowledge regarding the modern sensors,
suitable for water detection in its various states, the data
processing equipment, the theory of information and decision-
making, the methodology of data processing as well as the
specific communication systems. The structure of such a system
consists of:
- a central unit that represents the proper storing, processing and
analysis data systems;
- a network of ground sampling stations in which measurements
of the hydro-meteorological parameters are performed and
where a series of special measurement programs are carried on
(radiative characteristics of the snow in different conditions,
atmospheric parameters, etc.);
- communication channels with the reception satellite or with
the units that can supply such data, with the meteorological
radar network, with the specialized units in order to carry out
the aerial flights with the network of ground measurement
stations and with the users.
On its turn, the central unit behaves like a system composed by
subsystems. In this way, the main data inputs are received
through the telecommunication subsystem.
The achievement and operation of the open system implies:
- to ensure the data from high and mean resolution satellites,
from the radar network, as well as to ensure some repeated
flights for the basins of interest.
- to obtain the storing and processing technology of the image
data, and the conventional data transmitted in slow and rapid
flux;
- to create the data bank, to organize a GIS dedicated to the
surveillance and valuation of the water resources in the national
territory.
- to elaborate hydrological synthesis and prediction models that
accept the data resulted from the processing of remote sensing
information.
3. GIS APPLICATIONS IN SNOW HYDROLOGY
For many hydrological purposes remote sensing data alone are
not sufficient; they have to be merged with data from other
sources. This is a field where GIS's are extreme value. The
technique of merged information from different sources into
one system has to be carried out with great care. It is necessary
to use the same coordinate system, to work on the basis of equal
pixel size.
A combined remote sensing data base consisting of satellite,
aircraft data and digital terrain information derived from DEM
proved to be well suited in establish relationships between a
hydrological state vector and measurable hydrological
264
interdependent features of a basin (vegetation types and density
elevation slope and aspect of the relief).
GIS represent highly suitable opportunities for efficient
handling of large quantities of data. They allow the necessary
merging of remote sensing data with DEM as well as with other
hydro-meteorological data.
The GIS developed in the National Institute of Meteorology and
Hydrology for the snow cover water resources evaluation and
monitoring, in the Carpathian watersheds includes many
geocoded information organized in a complex related data base.
Data referring to the topography, organized in DEM (figure 1),
obtained from Shuttle Radar Topography Mission (SRTM),
land vegetal cover (figure 2), land use, soil types, hydro-
meteorological network, hydro-meteorological parameters, may
be used as separate layers or interconnected in order to extract
useful information for a correct and accurate estimation of snow
pack conditions and snow water resources, during the winter-
spring period.
f^ tí
f |
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Figure 1. Altitude levels derived from 90 m cell
SRTM DEM for Arges basin
Figure 2. Land cover derived from
LANDSAT 7 ETM- (04.07.2002)
The possibility of merging satellite imagery in the GIS allows
the use of updating spatial information for land cover, land use
and also for the evaluation of snow cover characteristics.
The DEM is very important for the evaluation of the
morphometric parameters of the watershed: the slope and
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