PowerPoint-PräsentationC) Results from nadir geometry (high spatial resolution)
D) Results from trace gas observations in limb geometry
(Why) do we need satellite observations?
Wish: ‘to measure everything everywhere’
=> Satellite observations are ‘closest’ to this ideal
• global observations: -remote areas can be ‚reached‘ -similar sensitivity over whole globe -comparison to models: test of our understanding of the system earth
• View from outside (philosophical & practical aspects)
• Separation of spatial and temporal variability
Verschiedene Beobachtungsgeometrien:
SCIAMACHY,...
SBUV, TOMS, GOME, SCIAMACHY, OMI, (A)ATSR, MISR, POLDER, SeaWiFS, MERIS, MODIS, .... ....Wettersatelliten...
Intrumente: SAGE, GOMOS, SCIAMACHY, ...
SCIAMACHY,...
SBUV, TOMS, GOME, SCIAMACHY, OMI, (A)ATSR, MISR, POLDER, SeaWiFS, MERIS, MODIS, .... ....Wettersatelliten...
Nur in Nadir-Richtung kann die Troposphäre sondiert werden
die planetare Grenzschicht kann sondiert werden (UV/vis)
(…dies ist der Bereich, in dem wir leben und in dem die meisten Quellen liegen!)
Vorteile des UV/vis Spektralbereiches:
Sputnik
Satellites
UV/vis nadir satellite history
If we want to observe the whole earth within a short period (e.g. few days)…..
…. polar orbits have to be chosen
….there is limited observation time at a given location
=> the number of photons is limited
Basic Limitations (I) (...there‘s not enough light!)
GOME on ERS-2 has 14 orbits per day
Assume that we get 1.5 Million photons from an area of 50 x 300 km²
50 km
300 km
1.5 Million photons
Assume that we get 1.5 Million photons from an area of 50 x 300 km²
50 km
300 km
=> Images, e.g. 10 000 photons per pixel
Assume that we get 1.5 Million photons from an area of 50 x 300 km²
50 km
300 km
Trade off between coverage an spectral and spatial resolution
Spatial Resolution of instruments with ‚high‘ spectral resolution
Spatial Resolution of instruments with ‚low‘ spectral resolution (e.g. MERIS: 0.3x0.3 km²)
MERIS image, Mt Etna, Sicily 28 March 2002 (c) ESA
Which horizontal resolution is actually needed?
Let‘s take a look into the atmosphere....
Trop NO2 SCIA VCD, January 2003 – June 2004, Steffen Beirle, IUP Heidelberg
CH4 model results from TM3 for August 2003 (J.F. Meirink)
Clouds above Russia, September 2004
Which horizontal resolution is actually needed?
Spatial resolutionlow high
......interestingly, these requirements match in general quite well with the (opposite) requirements on spectral resolution!
something here?
• Typically only column averaged quantities are derived
• Often some effects are masked by others, e.g. shielding by clouds
• Often decreased sensitivity close to the ground
Basic Limitations (III) Low temporal sampling
• For polar orbiting satellites only few overpasses
(one per day – one per 6 days)
• Usually observation for fixed local time
(full diurnal cycle is missed)
Nadir observations, high spatial resolution
-weather satellites (brightness => clouds and aerosols)
-different spectral channels yield information on aerosol particle size
-general problem: interference between surface reflectance and aerosol scattering
-observations at different angles
Early (and still succesful) UV/VIS concepts:
-Weather satellites (images)
Tiros 1 1960
Visible image, 27.01.2006 http://www.bom.gov.au/weather/satellite/
MODIS color image using 0.47, 0.55 &0.66 for blue green and red © Yoram Kaufmann
Dust Storm over the Red Sea
MODIS color image using 0.47, 0.55 &0.66 for blue green and red
True Color MODIS Surface Reflectance 500 meter Composite RGB
http://modis.gsfc.nasa.gov/gallery
Vegetation index from MODIS
wavelength [nm]
Landsat Channel 3
Landsat Channel 4
From observations in the red and near infrared spectral intervals vegetation can be monitored (e.g. Landsat, MODIS, etc.)
Early (and still succesful) UV/VIS concepts:
MODIS Enhanced Vegetation Index (Fall 2000)
http://modis.gsfc.nasa.gov/gallery
http://jeager.gsfc.nasa.gov/browsetool/
www.academic.emporia.edu
Sun glint © J.S. Aber
Composite map of the mean AOT at 0.659 μm retrieved using ATSR-2 data for February and March, 1999 over the INDOEX area. (G. de Leeuw)
High Spatial Resolution:
1.00 Wavelength / µm /
Spectral Aerosol Optical Thickness Day 057, 26. Feb. 2000
0.4
unaffected
Spectral ranges: over land: 6 channels 0.412 - 0.670 µm over ocean:8 channels 0.412 - 0.865 µm
investigation of different aerosol types
© W. v. Hoyningen-Hüne Retrieving Spectral Behavior of Aerosol Optical Thickness
Desert dust
Biomass burning
MODIS Aerosol optical thickness of coarse dust and fine pollution March 20, 2001
China
Korea
MODIS color image using 0.47, 0.55 &0.66 for blue green and red
MODIS aerosol optical thickness of dust and pollution
© Yoram Kaufman
Fine aerosol
Coarse aerosol
Two aerosol size modes
ATMOSPHÄREN- CHEMIE
Multi-angle Imaging Spectro-Radiometer (MISR) aboard NASA Terra
9 cameras: 1 nadir, 4 forward, 4 aftward zenith angles: 0, 26.1, 45.6,
60.0, 70.50
4 spectral bands: blue (446 nm) green (557 nm) red (672 nm) NIR (866 nm)
spatial resolutions: (camera and band dependent) 275 m, 1100 m
revisit time of a given path: 16 days.Time interval between 2 overpasses is 2-9 days © Johannes Keller
The POLDER instrument is a camera composed of a two- dimensional CCD detector array, wide field of view telecentric optics and a rotating wheel carrying spectral and polarized filters.
Polder: Optical thickness of the accumulation mode
(June 2003)
Observations in limb geometry
-long light paths through the atmosphere => high sensitivity
-the scattered light hasn’t reached deep atmospheric layers => only stratospheric measurements
-different viewing angles => information on different altitudes
Sven Kühl, Janis Pukite, IUP Heidelberg
AMF for 350nm
Inversion for O3
30.09.2004 24.08.2004
SCIA limb observations
In the Tropics limb profiles reach down into upper troposphere!
Inversion for O3