Innovative satellite aerosol validation

In order to understand and monitor global atmospheric aerosol variability and trends an integrated observation system is needed which comprises of accurate ground-based in situ and remote sensing instruments, regular airborne observations and satellite remote sensing. In this integrated system the satellite component provides the spatial coverage across the globe and between the stations. However, the mathematically ill-posed satellite aerosol retrievals have to rely on assumptions which are derived from ground-based and airborne measurements. Additionally, satellite inversions are indirect measurements and therefore need thorough validation. The validation against ground-based in-situ measurements of satellite-inverted total column aerosol properties beyond the total aerosol optical depth (AOD) has shown to be a challenging task. This is due to the different humidity state in the atmosphere and inside in-situ instruments and to the frequently complex layering of the atmosphere. In order to overcome these problems in a routine operation unmanned airborne vehicles (UAV) provide an opportunity for cost-effective regular three-dimensional in-situ observations to augment validation and to improve satellite retrievals. If on the long-term a number WMO-GAW aerosol stations can be equipped with such UAV routine observations, the in-situ satellite validation capacity will grow immensely. Several caveats have to be overcome (e.g. miniaturization and automatization of instruments, legal and technical constraints of UAV operation). As part of a feasibility study together with several partners and led by the Umweltforschungsstation Schneefernerhaus (UFS) the concrete requirements for UAV use in satellite aerosol validation at and around the Zugspitze with a downhill flight pattern will be specified in detail. A subsequent project is then planned to demonstrate this capability which could be extended in a future Virtual Alpine Observatory by investigating and implementing alternative UAV concepts.