20/1/2004 Dr. J.J. Remedios, Leicester. ACAW, 21/1/2004 1

GMES-GATO: Atmospheric correction using atmospheric composition satellite data

J.J. Remedios

EOS-SRC, Dept. of Physics and Astronomy, University of Leicester, U.K.

http://www.leos.le.ac.uk/home

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Structure

Influence of the atmosphere on surface observations

– Atmospheric correction

– Issues requiring surface and atmosphere information

Requirements for atmospheric correction

What are the technical issues?

Current developments?

Rational system needs (existing data/systems)

What is missing (future systems)?

GMES objectives

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Atmospheric influence on Systems Observing the Earth’ s Surface I

1. Satellite observations of the surface must intrinsically account for the atmosphere (atmospheric correction)

Atmospheric effects are present at almost all wavelengthsExample of 1. is correction of phytoplankton (ocean colour) data for

ozone contribution.

2. Atmospheric composition may also affect surface properties and also the reverse

– Direct e.g., chemical action, deposition, emitted flux of gases.

– Indirect, e.g., control of surface temperature or photosynthetic radiation.

User requirements include combined surface and atmosphere datasets, e.g., forestation and carbon dioxide, vegetation and water vapour, U/V radiation.

Example of 2. is dependence of phytoplankton concentrations on U/V radiation (and hence ozone)

Concentrate on 1 here: atmospheric correction

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SOURCES OF RADIATION AT THE TOP OF THE ATMOSPHERE; RADIATION BALANCE

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ATMOSPHERIC GASES AND THE SOLAR SPECTRUM

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Infra-red emission spectrum to space[Nadir signal for an i/r instrument

10 m 4 m20 m 5 m

Wavenumber = 1/ but in cm-1. Ref. pt. 10 m = 1000 cm-1

12 m window

8 m window

CO2O3

N2O, CH4

H2O

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I/R EMISSION SPECTRA

Sahara

Mediterranean

Antarctic

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Atmosphere influence on surface systems II

Policy issues in this area arise from two sources:• Requirements for atmospheric correction to surface data• Requirements for atmosphere data relevant to interpretation

of surface measurements. [cross-cutting BICEPS level]

Concentrate on 1 here.

User requirements for surface data can be grouped into three areas, for which a number of key issues can be identified.

• Environmental hazards [GMES]• Environmental monitoring [GMES]• Commercial remote sensing

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Volcanic Activity

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MODIS/AQUA – FIRES/AEROSOLMAY 9 2003

RUSSIA FIRES 2003

MOPITT CO. MAY 3-8 2003

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VEGETATION

ATSR-2 IMAGE:

VEGETATION DIFFERENCES AT THE BORDERS OF ISRAEL

ATSR-2 IMAGE:

DERIVED VEGETATION COVER (06/09/95)

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Atmospheric correction?

1. Most common atmospheric factors are

a) Clouds (troposphere – optically thick, thin, broken)

b) Tropospheric Aerosols (lower 2-3 km)

c) Tropospheric water vapour (lower 2-3 km)

d) Tropospheric CO2, CH4 (near-surface)

e) Molecular density (ground to approximately tropopause)

f) Stratospheric ozone (above 15/20 km)

g) Stratospheric aerosols (volcanic eruption)

h) O4 complex

2. Would also include ionosphere for radio/microwave

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1x1 Block:

Dual SST Matchups

• 30 June 2003

• Overpass ± 60 min

Key - matchups:

- within ± 0.3 K

X - > ± 0.3 K

- AATSR cloud

Increasing time

PUERTO RICO

Colour indicates dual-view SST

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ATSR2 SST (dual-nadir) vs TOMS Aerosol

DUAL-NADIR ATSR-2 SST

TOMS AEROSOL

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ATSR SST-AEROSOL: 07/1999

ATSR-2 VS AVHRR

TOMS AEROSOL INDEX

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Dust Storm over Red Sea(MODIS) August 14th 2003

http://naturalhazards.nasa.gov/

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Box14 Red Sea

Mean SST difference versus Time

TOMS Aerosol Index versus Time

Correlation=0.79

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Scatter Plot of Mean SST Difference versus Aerosol Index Over the Red Sea

Pixel by Pixel Correlation=0.544

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Schroedter, M., 1997 Diplomarbeit and M. Schrodter, F. Olesen, H. Fischer, 2003 IJRS

TOVS versus ECMWF profiles

Difference between LST: TOVS - ECMWF

Atmospheric correction

AVHRR 16.09.1992 afternoon

Bias TOVS vs. ECMWF 0.23 KStdv. TOVS – ECMWF 0.27 K

Black:clouds,water,snow

AVHRR 17.09.1992 afternoon

Bias TOVS vs. ECMWF 0.82 KStdv. TOVS – ECMWF 0.82 K

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Table of Requirements

Parameter λ region Typical λ Typical spatial resn.

Atmospheric correction requirements

Sea/land surface temperature

Infra-red 11 μm, 12 μm 3.7 μm (night)

1 x 1 km2 Aerosol, water vapour (T)

Surface reflectance/imagery

visible 470 nm -2.2 μm (discrete channels or low spectral resn.)

30 x 30 m2

to 5 x 5 m2

Aerosol, water vapour, ozone,

O4

Vegetation indices (derived from reflectance)

visible 600 nm – 1 μm 1 x 1 km2 Aerosol, water vapour, ozone

Ocean colour visible 400-550 nm 1 x 1 km2 Aerosol, water vapour, ozone,

O4

Sea/land surface height (SH)[single channel]

microwave

13.575, 5.3, 3.2 GHz

<2 x 2 km2 Water vapour0 cm (poles)-40 cm (tropics)

Ocean salinity microwave

1.4 GHz 35-50 x 35-50 km2

Water vapour

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Current and future developments

Current:

Hyperspectral

Multi-angle

Dedicated channels for atmospheric correction

Future:

Future instruments: potential for joint surface/atmosphere measurements (e.g., aerosols from imagers, H2O from SAR)

Role of assimilation models, e.g., ECMWF, KNMI Ozone

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What are the technical issues?

1. The latest sensors often incorporate a spectral channel for determining atmospheric correction factors.

a) Are all the relevant atmospheric factors measured

b) Is vertical resolution required?

c) Is the information measured at the correct wavelengths – particularly aerosols?

2. Surface products and imagers often require a high spatial resolution ( < 5 x 5 km2 ) with specific temporal resolution. What is the ability of atmospheric GMES systems to deliver this information?

Spectral vs Spatial resolution

3. Will atmospheric instruments measure the “correct” (relevant) types of aerosol?

4. What is the accuracy of assimilation and the potential for improved spatial scales?

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Rational System Needs (European)

1. Communication between surface sensing and atmospheric sensing communities (network)

2. Research into the exploitation of independent atmospheric sensing information within surface sensors.

3. Establish accuracies of ECMWF/ other assimilation systems for ozone/water vapour

4. Research into radiative transfer systems and models of the atmosphere

5. Inter-instrument research on aerosol across the e/m spectrum.

6. Operational data processing for multi-system data, e.g. ENVISAT/Metop

7. Continuity in the observation of key atmospheric variables and intercalibrated datasets relevant to surface products

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What is missing (in European systems)?

1. Research into the derivation of atmospheric correction information at high spatial scales.

2. Development of synergistic mission system concepts – formation flying

3. Development of assimilation systems providing atmospheric information to surface sensing communities

4. High spatial resolution aerosol mission to establish aerosol climatology/radiative properties [air quality]

5. [“Quick reaction” system for volcanic eruption into stratosphere]

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Overall surface-atmosphere system

An integration of surface and atmosphere systems:

• Observation systems

Use of atmospheric sensors in other GMES (sub-) system.

Exploitation of atmospheric information derived from other GMES systems (two-way)

High spatial resolution aerosol mission

Continuity of measurements for water vapour, ozone.

• Accessible and linked databases /processing centres [*]

• NRT capabilities including data assimilation [*]

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Volcanic Activity

(c) Dr. A. Richter, IFE/IUP Bremen

Andreas Richter and John Burrows – IUP Bremen

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Mt Etna