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 2000. Dedicated measurements simultaneous to satellite overpasses makesense 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 sensingrequire “good” spatial and spectral resolution. For that reason,SeaWIFs is presently the most promising candidate.Geostationary satellites have poor radiometric accuracy andspectral 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] andOption 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 exactlythe 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 exactlythe 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 extinctionprofiles) at several stations for validation of models that deriveaeosol 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 measurementsduring cloud free conditions from the existing EARLINET data basefitting to a SeaWIFs overpass.

Option 2: Aerosol Validation

Output:Several calibration points for the map of aerosol optical depthderived from (e.g.) v. Hoyningen-Huene’s SeaWIFs retrieval.

Information of special aerosol stratifications that might helpto explain possible deviations. E.g., check, whether algorithmworks 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 depthderived from (e.g.) v. Hoyningen-Huene’s SeaWIFs retrieval.

Information of special aerosol stratifications that might helpto explain possible deviations. E.g., check, whether algorithmworks 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 existsand 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 412 - 510 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 beforespring 2002. Sciamachy has a very poor spatial resolution.

Option 2: Aerosol Validation (contd.)

To be Discussed:

Data from stations not directly involved in this work packagewould 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 11-13 hours)? How many episodesshould 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 2000. Dedicated measurements simultaneous to satellite overpasses makesense 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 toinvestigate 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 presenceof Saharan dust layers in summer 2001 were provided.

Support Model Development

Actions: Supply of realistic vertical profiles of aerosol extinction toinvestigate 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 presenceof 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 (?)