Global Earth Observation and Monitoring
of the Atmosphere

WP 4.2: Integration of GEOmon data with satellite observation

For all the target parameters of GEOmon, valuable complementary satellite data series are available or will become available in the course of the project. For using them in synergy with the ground-based data, especially for assessing longterm trends, one has to deal with the problems inherent to satellite experiments. They have a finite lifetime and are subject to calibration problems, the data exhibit uncertainties originating in orbit/sampling properties, etc. The satellite data uncertainties and their information content needs to be fully characterised, before being able to combine multiplatform datasets for trend studies, and to integrate the data into assimilation models in support of the ground-based data.

Objectives

	Multi-dimensional characterisation of geophysical information retrievable from ground-based and satellite remote sensing techniques
	Development of “observation operators” to integrate ground-based and satellite remote-sensing observations
	GEOmon-based validation of complementary satellite data

Multi-dimensional characterisation of geophysical information retrievable from ground-based and satellite remote sensing techniques

Generally, observations of stratospheric compounds are of remote sensing nature, acquired either from the ground or from space. Remote sensing yields a smoothed and discrete perception of the real distribution and variability of atmospheric species. This perception
depends on the particular observation strategy and is different for different sensors. The integration of data from different sensors is hampered by differences concerning the vertical and horizontal resolution, geographical and vertical range, geographical and time sampling, and error budget.

We carry out a systematic multi-dimensional characterisation of the geophysical information actually probed by orbiting remote-sensing instruments addressed in GEOmon. We focus both on their potential capability to detect trends and on the possible integration/fusion of different remotely sensed data records. Information content studies address issues like the actual geolocation (centre and spread) of the measured information compared to the tangent point or the satellite footprint, resolution/smoothing aspects, contribution from a priori constraints in the retrieval, and geographical sampling properties that could affect data ingestion, like the azimuth of the probed air mass during a solar occultation measurement. The following observation techniques are addressed:

IR limb emission (MIPAS)
solar occultation in the IR (HALOE, ACE-FTS) and UV-VIS (SAGE, ACE-MAESTRO)
nadir IR emission (IASI)
nadir UV-VIS scattering (TOMS, GOME, SCIAMACHY, SBUV/2)
UV-VIS limb scattering (SCIAMACHY).

Reports about the multi-dimensional characterisation of information content of atmospheric data products retrieved from various remote-sensing instruments are be established and are available on demand.

Development of “observation operators” to integrate ground-based and satellite remote-sensing observations

Observational data usually are ingested into advanced integration tools through the use of the so-called “observation operators”. For the particular case of chemical data assimilation, the observation operator is a set of mathematical functions to be applied to the modeling results (usually, profiles of constituents produced on the model grid) to obtain quantities comparable to the observations. Thus far, observation operators have been limited to a quite simple interpolation scheme aiming mainly at reducing time and space differences between the measurement and the nodes of the assimilated field, assuming that the measured information is confined to the tangent point of the limb scan or to the satellite footprint of a nadir observation. We know that this assumption is inaccurate. We also know that similar conclusions apply to validation studies: meaningfulness of comparisons improves when the true properties of the retrieved information (incl. vertical and horizontal smoothing properties) are taken properly into account using satellite observation operators. The following observation operators for atmospheric data products are/will be available on demand for:

ground-based measurements
satellite measurements of infrared emission at limb
satellite measurements of nadir-scattered ultraviolet-visible light
satellite measurements of limb-scattered ultraviolet-visible light
satellite measurements of solar and stellar occultation
satellite measurements of infrared emission at nadir

GEOmon-based validation of complementary satellite data

For all the target parameters of GEOmon, valuable complementary satellite data series are available or will become available in the course of the project. For using them in synergy with the ground-based data as those provided within GEOmon, especially for assessing long-term trends, proper validation has to be performed. Drifts due to the satellite degradation in the harsh space environment, as well as time-varying or cyclic errors associated with atmospheric variability and orbiting/scanning properties will be quantified by correlative studies based on ground-based data records of known quality. The CALIPSO mission will contribute an original 3D view of stratospheric aerosols. Coordinated validation assessment is available on demand for:

satellite nitrogen dioxide data
satellite bromine monoxide data
satellite temperature data
satellite ozone data
CALIPSO aerosol and PSC data

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