ICAROHS Algorithm Theoretical Basis Document 1

ICAROHS ATBD1 consists of the following research topics:

- Algorithm Theoretical Basis Document HSRL based on the use of a Fabry Perot Etalon by A. Ansmann, D. Müller and U.Wandinger

- HSRL by vapour filter methods – Synthesis of HSRL techniques by M. Esselborn

-Probing the possibilities in retrieving aerosols beneath ice clouds by R. Buras, M. Fuchs, F. Filipitsch, and B. Mayer

-Creating realistic ECSIM scenes
by G.-J. van Zadelloff

The Algorithm Theoretical Basis Document ATBD1 of ICAROHS summarises the theoretical basis of the algorithms developed in the framework of ICAROHS. Driven by the complexity of the ICAROHS tasks, the ATBD is prepared as a compilation of standalone-
documents which, however, are inherently connected by the overall ICAROHS Project Structure.

The structure of ICAROHS is designed such that the algorithm development for HSRL methods is conducted in Task 2. This task is split into two branches in order to cover both HSRL methods applying vapour filters (DLR airborne lidar) and Fabry-Perot techniques (ESA ATLID). The task performed a sensitivity analysis of HSRL instrument
characteristics, processing errors, and errors introduced by the retrieval algorithms.
Resulting sub-algorithms for specific purposes such as sensitivity analyses were developed.
One of the largest benefits of ICAROHS is the combination of algorithm development and algorithm evaluation by direct comparison with field data. Observational data from various field studies are used to simulate scenes observed by a potential space-borne HSRL by means of the EarthCARE Simulator ECSIM and to compare the simulation results with field data from airborne HSRL and in-situ measurements and from groundbased Raman lidar measurements. The preparation of this data for ECSIM input is also part of Task 2. Furthermore, the evaluation of geophysical products accessible by multi-HSRL is performed within Task 2.