Images of measured radiance in different channels of the geostationary
Meteosat-9 SEVIRI instrument are analysed with respect to the
representativeness of the observations of eight cloud observatories in Europe
(e.g. measurements from cloud radars or microwave radiometers). Cloudy
situations are selected to get a time series for every pixel in a 300 km × 300
km area centred around each ground station. Then a cross correlation of each
time series to the pixel nearest to the corresponding ground site is
calculated. In the end a correlation length is calculated to define the
representativeness

Ebell, K.

Fischer, J.

Hünerbein, A.

Lindstrot, R.

Preusker, R.

Slobodda, J.

Atmospheric Measurement Techniques

Institutional Repository of the Freie Universität Berlin

Multichannel analysis of correlation length of SEVIRI images around ground-
based cloud observatories to determine their representativeness

Abstract. Images of the geostationary Meteosat-9 SEVIRI instrument during the year 2012 are analyzed with respect to the representativeness of the observations of eight cloud observatories in Europe. Cloudy situations are selected to get a time series for every pixel in a 300 km × 300 km area centered around each ground station. Then the Pearson correlation coefficient of each time series to the one of the pixel nearest to the corresponding ground site is calculated.  The area for which a station is representative is defined by the characteristic radius around each station for each SEVIRI channel, where the average correlation falls below 0.9. It is found that measurements in the visible and near infrared channels, which respond to cloud microphysics, are correlated in an area with a 1 to 4 km radius, while the thermal channels, that correspond to cloud top temperature, are correlated to a distance of about 20 km. The defined radius even increases for the water vapor and ozone channels. While all stations in Central Europe are quite alike, the correlations around the station in the mountains of southern Italy are much lower. Additionally correlations at different distances corresponding to the grid box sizes of forecast models were compared. The results show good comparability between regional forecast models (grid size &amp;amp;lesssim; 10 km) and ground-based measurements since the correlations in less than 10 km distance are in all cases higher than 0.8. For larger distances like they are typical for global models (grid size &amp;amp;gtrsim; 20 km) the correlations decrease to 0.6, especially for shortwave measurements and corresponding cloud products. By comparing daily means, the characteristic radius of each station is increased to about 3 to 10 times the value of instantaneous measurements and also the comparability to models grows.
                        </jats:p

J. Slobodda

A. Hünerbein

R. Lindstrot

R. Preusker

K. Ebell

J. Fischer

Crossref

Multichannel analysis of correlation length of SEVIRI images around ground-based cloud observatories to determine their representativeness

Images of measured radiance in different channels of the geostationary Meteosat-9 SEVIRI instrument are analysed with respect to the representativeness of the observations of eight cloud observatories in Europe (e.g. measurements from cloud radars or microwave radiometers). Cloudy situations are selected to get a time series for every pixel in a 300 km × 300 km area centred around each ground station. Then a cross correlation of each time series to the pixel nearest to the corresponding ground site is calculated. In the end a correlation length is calculated to define the representativeness.

It is found that measurements in the visible and near infrared channels, which respond to cloud physical properties, are correlated in an area with a 1 to 4 km radius, while the thermal channels, that correspond to cloud top temperature, are correlated to a distance of about 20 km. This also points to a higher variability of the cloud microphysical properties inside a cloud than of the cloud top temperature. The correlation length even increases for the channels at 6.2, 7.3 and 9.7 μm. They respond to radiation from the upper atmospheric layers emitted by atmospheric gases and higher level clouds, which are more homogeneous than low-level clouds.

Additionally, correlations at different distances, corresponding to the grid box sizes of forecast models, were compared. The results suggest the possibility of comparisons between instantaneous cloud observations from ground sites and regional forecast models and ground-based measurements. For larger distances typical for global models the correlations decrease, especially for short-wave measurements and corresponding cloud products. By comparing daily means, the correlation length of each station is increased to about 3 to 10 times the value of instantaneous measurements and also the comparability to models grows

Repositorium für Naturwissenschaften und Technik

English

Abstract. Images of measured radiance in different channels of the geostationary Meteosat-9 SEVIRI instrument are analysed with respect to the representativeness of the observations of eight cloud observatories in Europe (e.g. measurements from cloud radars or microwave radiometers). Cloudy situations are selected to get a time series for every pixel in a 300 km × 300 km area centred around each ground station. Then a cross correlation of each time series to the pixel nearest to the corresponding ground site is calculated. In the end a correlation length is calculated to define the representativeness.  It is found that measurements in the visible and near infrared channels, which respond to cloud physical properties, are correlated in an area with a 1 to 4 km radius, while the thermal channels, that correspond to cloud top temperature, are correlated to a distance of about 20 km. This also points to a higher variability of the cloud microphysical properties inside a cloud than of the cloud top temperature. The correlation length even increases for the channels at 6.2, 7.3 and 9.7 μm. They respond to radiation from the upper atmospheric layers emitted by atmospheric gases and higher level clouds, which are more homogeneous than low-level clouds.  Additionally, correlations at different distances, corresponding to the grid box sizes of forecast models, were compared. The results suggest the possibility of comparisons between instantaneous cloud observations from ground sites and regional forecast models and ground-based measurements. For larger distances typical for global models the correlations decrease, especially for short-wave measurements and corresponding cloud products. By comparing daily means, the correlation length of each station is increased to about 3 to 10 times the value of instantaneous measurements and also the comparability to models grows.
                    </jats:p

Images of measured radiance in different channels of the geostationary
Meteosat-9 SEVIRI instrument are analysed with respect to the
representativeness of the observations of eight cloud observatories in Europe
(e.g. measurements from cloud radars or microwave radiometers). Cloudy
situations are selected to get a time series for every pixel in a
300 km × 300 km area centred around each
ground station. Then a cross correlation of each time series to the pixel
nearest to the corresponding ground site is calculated. In the end a
correlation length is calculated to define the representativeness.

It is found that measurements in the visible and near infrared channels,
which respond to cloud physical properties, are correlated in an area with a
1 to 4 km radius, while the thermal channels, that correspond
to cloud top temperature, are correlated to a distance of about
20 km. This also points to a higher variability of the cloud
microphysical properties inside a cloud than of the cloud top temperature.
The correlation length even increases for the channels at 6.2,
7.3 and 9.7 μm. They respond to
radiation from the upper atmospheric layers emitted by atmospheric gases and
higher level clouds, which are more homogeneous than low-level clouds.

Additionally, correlations at different distances, corresponding to the grid
box sizes of forecast models, were compared. The results suggest the
possibility of comparisons between instantaneous cloud observations from
ground sites and regional forecast models and ground-based measurements. For
larger distances typical for global models the correlations decrease,
especially for short-wave measurements and corresponding cloud products. By
comparing daily means, the correlation length of each station is increased to
about 3 to 10 times the value of instantaneous measurements and also the
comparability to models grows

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https://refubium.fu-berlin.de/bitstream/fub188/16376/1/amt-8-567-2015.pdf

Multichannel analysis of correlation length of SEVIRI images around ground- based cloud observatories to determine their representativeness

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