WP 8: Impact on Satellite Retrievals

University of l’Aquila (DFUA [12])

Ecole Polytechnique (EPFL [13])

Observatory of Neuchatel (ON [14])

Partners (according to Contract):

Meteorol. Inst. Munich (MIM [17]): Matthias Wiegner

Overview over Presentation

1. EARLINET-Contract: Workpackage 8

2. Relevance of WP 8

3. Contributions to WP 8

Definition

Examples

4. Conclusions

EARLINET-Contract:

1. Quantify the sensitivity of radiances at the top of the atmosphere (toa) to variations of the aerosol distribution [...]. This will be used to provide an estimate of the impact of aerosols on retrievals [...] from spaceborne platforms.

2. Provide aerosol distributions for calibration purposes upon request [...].

Contract: Objectives and input of WP8

Contract: Description of work

This is done by running adequate radiative transfer models using the aerosol data [...]. As a result, inversion algorithms [...] can be critically reviewed and improved.

Additional lidar measurements [...] will be performed at special occasions when satellite overpasses close to an EARLINET station occurs [...]. For this part to stay within the limits of the available resources it will be done only on request.

Relevance of WP 8

multispectral and multiangular radiances from satellites used to retrieve aerosol optical depth

critical over land surfaces (albedo, orography)

complex retrieval algorithms require validation

„Validation of atmospheric parameters“

Relevance of WP 8

multispectral and multiangular radiances from satellites used to retrieve surface properties (e.g. precision farming)

determine atmospheric influence (unknown aerosol effect)

corrections of atmospheric masking require input and validation

„Validation of surface parameters“

Relevance of WP 8

Radiative transfer calculations required to understand satellite data

aerosol distribution is one controlling parameter

contribution of lidar data to be assessed

„Improvement of aerosol understanding“

Three contributions to WP 8

Demonstrate the benefit of lidar data on the basis of dedicated experiments

Note: WP‘s ordered by „time allocated“:WP8 is 15. out of 20.

Offer our datasets to the satellite communityfor validation purposes

Identify cases where lidar data are useful

First contribution

Actions proposed: Supply survey of available aerosol extinction profiles (site, time, wavelength)

Goal:Support validation of satellite retrievals by supplying lidar data

(possible candidates: Envisat, MSG community)

Data dissemination:On request (Webpage)

First contribution

Results/Conclusions:Aerosol extinction profiles from more than 20 lidar stations, twotimes a week and for more than two years, are available.

Validation of aerosol retrievals requires a careful selectionof time and place, and averaging over reasonable periods.

Envisat and MSG are still at the beginning of their operation times. Final success requires extra funding (also for the satellitecommunity), time horizon: 2003/04

“Seed is set, but harvesting takes time”

Three contributions to WP 8

Demonstrate the benefit of lidar data on the basis of dedicated experiments

Note: WP‘s ordered by „time allocated“:WP8 is 15. out of 20.

Offer our datasets to the satellite communityfor validation purposes

Identify cases where lidar data are useful

Acquisition mode:CHRIS: 18 km swath, 25 m resolution, 19 spectral bands, along track (5 angles)

Second contribution

Time and Place: May, June, July and August 2002 in Gilching

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.

Second contribution

Results/Conclusions:

Satellite PROBA encountered severe problems: no data areavailable up to now.

First data are announced for fall this year.

A new special field campaign is difficult to be organised.

Three contributions to WP 8

Demonstrate the benefit of lidar data on the basis of dedicated experiments

Note: WP‘s ordered by „time allocated“:WP8 is 15. out of 20.

Offer our datasets to the satellite communityfor validation purposes

Identify cases where lidar data are useful

Third contribution

Actions: Performing model calculations with realistic aerosol extinction profiles to investigate the influence of aerosols on toa-radiances

Goal:

Support model development by supplying lidar data

Variation of aerosol optical depth

Variation of aerosol type

Variation of aerosol (vertical) distribution

Variation of surface albedo

Variation of solar zenith angle

Fixed wavelength (532 nm)

Radiative transfer calculations

Verticalaerosol distribution:

5 cases

(1) (2) (3) (4) (5)

Model calculations

Normalized to isotropic radiance „Anisotropy-Function“

Radiances at top of atmosphere

as a function ofsurface albedofor different aerosoloptical depths

fixed aerosol type,aerosol profile andsolar zenith angle

Radiance/flux at toa

different aerosol type

Radiance/flux at toa

Radiance/flux at toa

different aerosol type

Radiance/flux at toa

different aerosol type

Radiance/flux at toa

different aerosol type

Radiance/flux at toa

same as before: 32.50

Radiance/flux at toa

now: 62.50

Radiance/flux at toa

as a function ofsurface albedofor different aerosoltypes

fixed optical depth,aerosol profile andsolar zenith angle

Radiance/flux at toa

Different optical depth

Radiance/flux at toa

Different optical depth

Radiance/flux at toa

Different optical depth

Radiance/flux at toa

Different optical depth

Radiance/flux at toa

as a function ofsurface albedofor different aerosolprofiles

fixed optical depth,aerosol type andsolar zenith angle

Radiance/flux at toa

Different aerosol type

Radiance/flux at toa

Different aerosol type

Radiance/flux at toa

Different aerosol type

Radiance/flux at toa

Different aerosol type

Radiance/flux at toa

as a function ofsurface albedofor different aerosolmixtures

fixed optical depth,aerosol types andsolar zenith angle

Radiance/flux at toa

Different aerosol type

Radiance/flux at toa

Different aerosol type

Radiance/flux at toa

Different aerosol type

Radiance/flux at toa

Different aerosol type

Radiance/flux at toa

Different layer width

Conclusions from the model simulations

Satellite radiances are significantly influenced by aerosols:

-- optical depth-- aerosol type-- aerosol profile

Conclusions from WP 8

Validation campaigns of aerosol parameterswith lidar data require extra efforts

Model simulations show that the aerosol vertical distribution is a second order effect for satelliteremote sensing, but should be provided together with a aerosol classification („aerosol type“)

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