Validation by ground-based DOAS measurements
Since the launch of the SCIAMACHY instrument on board of ENVISAT,
a network of ground-based instruments is being used to validate the SCIAMACHY lv2-data. One central component of this network are
zenith-viewing UV/visible DOAS instruments measuring total columns of O3, NO2, BrO, OClO,
and a number of other trace species. As part of the German SCIAMACHY and GOME
validation activities, the University of Bremen operates the
BREDOM network which consists of
several existing DOAS instruments at high and middle latitudes and two additional instruments deployed for the SCIAMACHY
validation at low latitudes, a region of high interest for atmospheric dynamics and chemistry that up to now has very stations
that can be used for the validation of satellite experiments.
Once set-up, zenith-sky viewing DOAS instruments can be operated
continuously and with little maintenance needed. They therefore are well suited for long time series and continuous validation of
satellite measurements. Over time, a large number of coincident measurements under different atmospheric conditions
accumulates and can be analysed not only to access the accuracy of the satellite measurements, but also to determine possible
reasons for problems in the SCIAMACHY data. This is particularly true if measurements from many stations is analysed as has been
demonstrated during the GOME validation campaigns.
A summary of the results from the ground-based DOAS validation activities at the University of Bremen can be found in
Validation by airborne DOAS measurements
In addition to the long-term ground-based measurements, latitudinal and longitudinal transsects from airborne platforms are useful for the validation of satellite products. consequently, one project within the German contribution to SCIAMACHY validation dealt with Airborne Multi Axis DOAS (AMAXDOAS) measurements from the DLR Falcon, a joint activity of the University of Bremen and the University of Heidelberg. The advantage of airborne measurements is the quasi instantaneous validation of a large number of satellite measurements under varying conditions. In addition, the AMAXDOAS measurements provide a direct validation of tropospheric columns, in particular for NO2 (see paper by K.-P. Heue et al. below).
Some results from the airborne DOAS validation activities at the University of Bremen can be found in