|
|
The observations used for the analysis of
the atmosphere can be divided roughly into conventional, in-situ
observations and non-conventional, remote-sensing
observations.
The conventional observations consist
of direct observations from surface weather stations, ships, buoys,
radiosonde stations and aircraft, both at synoptic and,
increasingly, at asynoptic hours. All surface and mean
sea-level-pressure observations are used, with the exception of
cloud cover, 2 m temperature and wind speed (over land). 2 m
temperature and dew point observations are used in the analysis of
soil moisture. Observed winds are used from ships and buoys but not
from land stations, not even from islands or coastal stations.
The non-conventional observations are
achieved in two different ways: passive technologies sense
natural radiation emitted by the earth and atmosphere or solar
radiation reflected by the earth and atmosphere; active
technologies transmit radiation and then sense how much is
reflected or scattered back. In this way surface-wind vector
information is, for example, derived from the influence of the
ocean capillary waves on the back-scattered radar signal of
scatterometer instruments (Hersbach and Janssen, 2007).
|
