WP 8: Impact on Satellite Retrievals University of l’Aquila (DFUA [12]): Vincenzo Rizi Ecole Polytechnique (EPFL [13]): Bertrand Calpini Observatory of Neuchatel (ON [14]): Valentin Mitev Partners (according to Contract): Met. Institute Munich (MIM [17]): Matthias Wiegner I have to apologize for my absence; I tried the “Jan Ullrich Loop” but my collar-bone didn’t like it.

The goal of Workpackage No. 8 includes the modeling of the aerosol influence on radiances measured by satellites and the provision of additional lidar measurements on request. What does this mean? Measurements: Lidar data are available since May Dedicated measurements simultaneous to satellite overpasses make sense if pixel are small and cloud free conditions can be guaranteed. On the other hand, the existing data base can be used for validation of satellite measurements and their products. Model calculation: Models for atmospheric corrections (e.g., to retrieve surface properties) and models to derive aerosol properties can be supported by supplying lidar data. Remark: The development of such models itself is beyond the scope of EARLINET. Both “classes” are linked and cannot be considered separately. Goals of the Work-Package

EARLINET and Satellites General remarks: Meteorological satellites suitable for aerosol remote sensing require “good” spatial and spectral resolution. For that reason, SeaWIFs is presently the most promising candidate. Geostationary satellites have poor radiometric accuracy and spectral resolution, GOME et al. have very poor spatial resolution, Landsat et al. have very poor temporal sampling, and sensors with very high spatial resolution are not yet in orbit (MERIS [250 m], Chris et al. [25 m]). Thus, we follow two options: Option 1: plan dedicated experiments on the “compare same atmospheric volume”-concept [risk: overcast conditions] and Option 2: select data sets already available on the “validate aerosol parameters”-concept

Acquisition mode: CHRIS: 18 km swath, 25 m resolution, 19 spectral bands, along track (5 angles) Option 1: dedicated measurements for sensor calibration Time: PROBA/CHRIS shifted to 2002 Location: Gilching near Munich and Rhine valley In co-operation with: Goal: Full characterization of surface and atmosphere of exactly the same scene (for calibration of satellite sensor and algorithms) Requirements: co-incidence and co-location and very small satellite pixel required.

Acquisition mode: CHRIS: 18 km swath, 25 m resolution, 19 spectral bands, along track (5 angles) Option 1: dedicated measurements for sensor calibration Time: PROBA/CHRIS shifted to 2002 Location: Gilching near Munich and Rhine valley In co-operation with: Goal: Full characterization of surface and atmosphere of exactly the same scene (for calibration of satellite sensor and algorithms) Requirements: co-incidence and co-location and very small satellite pixel required.

Option 2: aerosol validation with existing data Actions proposed: Supply of aerosol optical depths (derived from lidar extinction profiles) at several stations for validation of models that derive aeosol optical depth from SeaWIFs data (other aerosol products are not available). Possible co-operation with University of Bremen (v. Hoyningen-Huene) Goal: Support model validation by supplying lidar data Data: Select suitable co-incident, high qualitity lidar measurements during cloud free conditions from the existing EARLINET data base fitting to a SeaWIFs overpass.

Option 2: Aerosol Validation Output: Several calibration points for the map of aerosol optical depth derived from (e.g.) v. Hoyningen-Huene’s SeaWIFs retrieval. Information of special aerosol stratifications that might help to explain possible deviations. E.g., check, whether algorithm works in the presence of Saharan dust layers. Provision of information of the aerosol type (if possible, e.g., from trajectories, lidar data themselves, auxiliary data) to support satellite retrieval algorithm (input for them). Possible co-operation with University of Bremen (v. Hoyningen-Huene)

Option 2: Aerosol Validation Output: Several calibration points for the map of aerosol optical depth derived from (e.g.) v. Hoyningen-Huene’s SeaWIFs retrieval. Information of special aerosol stratifications that might help to explain possible deviations. E.g., check, whether algorithm works in the presence of Saharan dust layers. Provision of information of the aerosol type (if possible, e.g., from trajectories, lidar data themselves, auxiliary data) to support satellite retrieval algorithm (input for them). Possible co-operation with University of Bremen (v. Hoyningen-Huene)

Option 2: Aerosol Validation (contd.) Background Information: A SeaWIFs algorithm to derive aerosol optical depth exists and has been (successfully) applied. SeaWIFS has a spatial resolution of about 1 km and a coverage of 1800 km (swath width); similar to AVHRR Algorithm works best in the spectral range between nm (surface is dark); lidar data of 532 nm can be extrapolated. Times to be compared should be in spring and early summer (green vegetation; no problems with water stress) MERIS will have a better resolution but will be available not before spring Sciamachy has a very poor spatial resolution.

Option 2: Aerosol Validation (contd.) To be Discussed: Data from stations not directly involved in this work package would be required. Is that possible? Who will calculate the optical depth from the extinction profiles (owner or M.W.)? Is an extra qualitity check required/desired by the owner of the data? Selection of episodes from the diurnal cycle subset (best time of the day is hours)? How many episodes should be selected (one, two, more?) Should we include algorithms to derive aerosol optical depth over land from other institutes (answer from Berlin is pending)?

The goal of Workpackage No. 8 includes the modeling of the aerosol influence on radiances measured by satellites and the provision of additional lidar measurements on request. What does this mean? Measurements: Lidar data are available since May Dedicated measurements simultaneous to satellite overpasses make sense if pixel are small and cloud free conditions can be guaranteed. On the other hand, the existing data base can be used for validation of satellite measurements and their products. Model calculation: Models for atmospheric corrections (e.g., to retrieve surface properties) and models to derive aerosol properties can be supported by supplying lidar data. Remark: The development of such models itself is beyond the scope of EARLINET. Both “classes” are linked and cannot be considered separately. Goals of the Work-Package

Support Model Development Actions: Supply of realistic vertical profiles of aerosol extinction to investigate the influence (and relevance) of aerosol stratification on top-of-the-atmosphere-radiances (atmospheric masking) In co-operation with: Goal: Support model development by supplying lidar data Data: Special measurements over Munich during the presence of Saharan dust layers in summer 2001 were provided.

Support Model Development Actions: Supply of realistic vertical profiles of aerosol extinction to investigate the influence (and relevance) of aerosol stratification on top-of-the-atmosphere-radiances (atmospheric masking) In co-operation with: Goal: Support model development by supplying lidar data Data: Special measurements over Munich during the presence of Saharan dust layers in summer 2001 were provided.

Deliverables April 2002 and February 2003: Report on aerosol impact on satellite retrievals Timeframe of WP 8 Start: May 2000 End: December 2002 Other Deadlines May 2002: Contribution to Annual Report August 2001: Quality Assurance Report (?)