International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B7. Istanbul 2004
models, The selection of appropriate sensor depends on a trade-
off between spatial and temporal resolution (Rott, 1987).
This paper describes the results of a study undertaken over two
high mountainous alpine catchments in north caslern part off
Italy. the aim of which was to assess the suitability of remote
sensing satellite data for hydrological forecasting, For this
purpusc. vistble and infrared digital data from multi temporal
Landsat MSS and TM sensors has been used for snow cover
monitoring and snowmelt runoff forecast.
2. AREA OF INVESTIGATION
The study area is located in the Dolomiti Mountains of the
north-castern Halian Alps and is enclosed between latitudes 46?
23 ' N and 46" 33'N and longitudes 117 47°E and 12° WE.
Fhere ure two catchments known as Cordevole and La Vizza in
this region. Both are drained by the main river Cordevole. The
area of Cordevole river basin measures 248 km? with a mean
altitude of 1900 m above sca level (Fig.1).
Figure 1 Physiographical map of Cordevole river basin
Ihe La Vizza basin is a small catchment extending to 7,5 km“
Its elevation ranges from 1800 meters above mean sca level to
3150 meters above mean sea level (Fig.2).
Figure 2 Physiographical map of La Vizzu basin
Both the watersheds are characterized by the very low
permeability geological formations of the arca known as
calcareous dolimitic rocks, The normal annual rainfall in this
region is around 1070 mm. The hydrological regime shows a
maximum water [low during the late spring and early summer
and a minimum during the winter.
3. GROUND DATA
There are three well-equipped — hydro-meteorological
observatories located at Arabba (1620 masl), Andraz (1400
masi) and Caprile (1000 masl) in the area. At all these
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observatories precipitation (both. rain and snow] data and
incoming solar radiation are collected every tive minutes, while
wind direction and wind speed are monitored at ten-minute
intervals. The air temperature and relative humidity are also
measured at hourly intervals, in addition lo daily maximum and
minimum air temperatures. These observatories are maintained
by Centro Sperimentale Valanghe e Difesa ldrogeologica
Regione Veneto (CSVDI) which is a research center for
avalanches and hydrological control located at Arabba. Ihe
[talian National Authority for Energy (Ente Nazionale per
"Energia Elettrica — ENEL), which maintains a hydropower
station at Lake Alleghe., computes discharges of the Cordevole
River from water level measurements of the lake (Fig. 3). These
discharges are corrected for water pumping carried out by the
hydropower station, The computed discharges are in good
agreement with the historical discharges of the river measured
using conventional hydrological methods. For La Vizza
catchment. the discharge measurements at the basin out let, La
Vizza station which is at an altitude of’ 1804 meters above mean
sca level are made hy sharp crested weir with continuous
digital recording equipment. The Arabba hydro-meteorological
observatory 1s about 2 km fram the outlet on the downstream
ide.
ui
53 ARN
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CAE a
Figure 3 Discharge station at Caprile
Ground truth campaigns have been carried out twice coinciding
with satellite passes over the area ol investigation. The
information was recorded on a number of black and white
photographs. Some of the general observations on the first field
campaign in April indicated that the catchment. upstream. of
Arabba was uniformly covered with snow except on south-
facing slopes where some pasture land had started to appear.
On the downstream side of Arabba south-facing slopes were up
to 70% snow free while those facing north were uniformly
covered with snow. This was owing to the fact that in the
middle latitudes of the northern hemisphere, hills that face
would reccive morc sunshine and hence become warmer than
the partly shielded north-facing hills. Conscquently snow
usually lingers on the ground for a longer time on north-facing
slopes than on the warmer south facing slopes. The variation of
snow depth and intensity af melt are abserved to be dependent
on altitude and discontinuous snow cover occurred at several
melting regions in the basin. The break-up of snow cover was
observed to be rapid at lower altitudes: the satellite sensor
observes these areas as a mixture of snow-covered and snow-
free terrain. Hence. at low altitudes mixed pixels prevail and at
high altitudes pure pixels exist. Thé ratio of snow-covered to
