Report on quality and performance of interpolated BLH retrieval product and cross-validation method

One of WP3 objectives is to demonstrate the contribution of lidar equipping ICOS to diagnose boundary layer height (BLH). BLH is a critical variable that defines the dilution of CO2 and CH4, emitted or taken up at the surface, in the atmosphere. Two atmospheric boundary layer retrieval algorithms have been selected in WP3 (PyBL & STRAT), and the choice was made to have them improved by their respective developers (resp. MPG & CNRSLMD) to meet the specific needs of ICOS-INWIRE in terms of BLH restitution and implementation on site in the ICOS network (see MS7, Develop reference implementation for unified pre-processing and BLH retrieval algorithm). It results in two adapted versions (PyBL_ICOS & STRAT+) of original algorithms that are compared to each other in a first part of this deliverable, over a common dataset of measurement, thanks to standard data format for backscatter signals from lidar/ceilometers defined in MS6. Since optical systems will not necessarily be exactly collocated with atmospheric stations in the ICOS network, spatial interpolation of mixing heights is investigated in a second part of this deliverable. Two interpolation schemes (distance-based and geo-statistical) are tested. In particular results of kriging methods with mixing heights from atmospheric model to physically constrain the interpolation are presented. In a last part, quality and performance of BLH retrieval are studied. In particular lidar/ceilometer sensitivity for BLH retrieval is addressed, and cross validation of BLH retrievals by ceilometers versus micro wave radiometer and radiosondes mixing heights is shown.