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Remote sensing for resources development and environmental management
Damen, M. C. J.

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Figure 2: Location of the in situ
stations used in verifi
cation study.
department of KNMI has performed some in-situ
measurements on the North Sea. "Bucket"-
temperatures are menasured at ± 30 stations (see
fig. 2). These measurements are compared with AVHRR
derived SST's. The date of the NOAA-9 image was
October 25, 3-00 GMT.
The in-situ measurements started on October 28,
15.00 GMT and ended on the 30 th , 5.00 GMT.
The SST's were also calculated using coefficients
determined by McClain (1981). Figure 2 shows the
in-situ measurements along with the two different
satellite SST's retrievals. This graph shows that
the in-situ spatial structure is well represented
by the satellite derived SST's and also that the
Rutherford coefficients perform slightly better
than the McClain coefficients. The difference
between in-situ measurements and satellite derived
SST is never larger then 0.55 for the Rutherford
coefficients: the mean bias being -0.064 and the
RMS 0.244. For the Mcclain coefficients the
statistics are: max. difference is 0.73; mean bias
is 0.022 and RMS 0.292.
These statistics are in good agreement with
published results (Minnett et al, 1984).
4.2. Land surface temperature (LST)
4.2.1. Techniques
For the development of a method to derive LST's out
of AVHRR-thermal IR-data two more problems, except
for the atmospheric correction arise:
1. the variable emissivity of land surface.
2. Lack of suitable groundtruth data.
Price (1984) has demonstrated that the use of split
window techniques originally developed for SST's,
can also be used for the calculation of true LST's.
He estimated a 2-3 K error in the estimates of
LST's, using a SST- split window technique mainly
caused by uncertainties ih the emissivity small
compared to satellite-observed temperature
variations in a certain region.
t s (c)
: in situ "bucket" temperatures
» « * split window SST (Rutherford coefficients)
• « : Ü „ „ (McClain „ )
Figure 3: Results of verification study for
split window SST's.
Oxford, U.K. we investigated the relation between
split-window LST's and "screen"-temperatures,
measured at meteorological stations. A data-set
(day and night NOAA-9 imagery and meteorological
data of the same times) for the period 14-20 April
1985 was used. The stations involved are nearly all
located in the U.K.. LST was calculated, using the
Rutherford coefficients. It must be added that in
general, differences between screen- and land
surface temperatures will depend heavily on the
actual weather conditions, the nature of the
underlying surface and the type of vegetation
cover. This makes the relation rather complicated
and variable in space and time. The situation is
still further complicated by the fact that the
screen temperature measurements are point
measurements whereas the LST's are representive for
an area of approx. 1x1 km . this all renders the
correlation between the two temperatures rather
poor (regression coefficient 038). However
byaveraging the surface- and air temperatures, of
all cloudfree stations at a certain date, it can be
shown that the average difference between surface-
and screentemperature is fairly steady from day to
day (see fig. 4).
- Digital AVHRR-imagery can suitable be processed
in an automatic way to provide Earth-surface
- The development of the "channel 4- channel 5"-
technique turned out to be a valuable addition
to available cloud clearing algorithms
identifying thin cirrus clouds litherto going
- Limited research at KNMI has demonstrated that
the AVHRR can deliver relatively accurate
surface temperatures (especially for sea
surface), suitable for use in various
- KNMI now has as the only institute in the
Netherlands the software available to perform
all the necessary steps in the automatic
processing of AVHRR-imagery.
4.2.2. Validation
In co-operation with the Met. Office Unit in
Harries, J.E.,Llewellyn-Jones, D.T., Minnett, P.J.,
Saunders, R.W. and Zavody, A.M., 1983.
Observations of sea-surface temperature for