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Transcript of RADIATION AND REMOTE SENSING Radiation Tutorial PORSEC 2010 1 Tutorial lecture in Keelung, Taiwan,...
RADIATION AND REMOTE SENSING
Radiation Tutorial PORSEC 20101
Tutorial lecture in Keelung, Taiwan, PORSEC 2010
by
Kristina B. KatsarosAdjunct Professor, University of Miami
Former President of PORSEC Association (2004-2008)
Email: [email protected] used from:
Prof. Rachel Pinker, University of Maryland, Prof. Mark Bourassa, Florida State University, and Textbook by Prof. Ian Robinson (see further
reading)
RADIATION AND REMOTE SENSING
Radiation Tutorial PORSEC 20102
Aspects covered:1)Background/history2)Spectral bands; visible, infrared,
microwave2) Radiative fluxes in the oceanic heat
balance and some equations3) Method for radiative transfer
estimates4) Satellites instruments, systems and methods of sampling for fluxes
(examples)5) Importance of microwave radiometry
for flux estimates 6) Photo-synthetically Active Radiation,
PAR7) Further reading, web-sites…
Radiatwill be provided.ion Tutorial PORSEC 2010
3
About the course material to follow
The incoming solar radiation from the sun (insolation) that reaches the Earth’s surface (about 50% of that emitted from the sun and received at the planet's distance from the sun) determines the exchange of energy between the land, sea and the atmosphere and consequently, controls climate.
Outgoing infrared radiation keeps the Earth’s temperature in balance with the solar energy absorbed, but this is a long story involving radiative gases. Visible and short infrared radiation (from he sun) and long infrared radiation ( from Earth ) are measured directly at the top of the atmosphere (TOA) and atmospheric, radiative transfer models are applied to infer the radiative balance at the sea surface. For this, information on cloud effects are required and here microwave radiation sensors have also come to contribute.
Environmental satellites have for decades provided observations of the various components of atmospheric, cloud and surface radiative properties.
We will only be able to touch on a few aspects of this rich history in this lecture, but a reading list
Oceanographic applications include estimates of net air-sea energy flux related to monitoring of oceanic heat content, mixing and buoyancy processes. The net air-sea flux and the division between the flux components is important when forcing numerical models of ocean circulation.Methodologies for obtaining such information by remote sensing, accuracy of such estimates, and current status of data availability will be given. Applications in hydrological studies and climate research are many. Links to international activities abound. Photosynthesis depends on solar radiation
Radiation Tutorial PORSEC 20104
Radiation Tutorial PORSEC 20105
Graphic of ocean’s role in Climate
Illustration of air-sea interactions
Radiation Tutorial PORSEC 20106Bourassa 08 /
Electromagentic spectrum
Radiation Tutorial PORSEC 20107
Components of Net Radiative Transfer
Radiation Tutorial PORSEC 20108
Terrestrial Radiation- Emitted by bodies at Earth’s temperatures (around 300K)Relatively non-energetic (long wavelength) photonsSpectrum includes infra-red and longer wavelengths
E = h E = Energy per photon; c = h = constant; = frequency E = h c / c = speed of light; = wavelength
Solar Radiation-Emitted from very hot bodies (e.g., the sun, red or white
hot objects), sun’s temperature at our distance corresponds to 5,000K
-Relatively energetic (short wavelength) photons-Spectrum includes visible light and shorter wavelengths
Radiation Tutorial PORSEC 20109
Radiation Tutorial PORSEC 201010
Considerations in the Radiative Budget
Radiation Tutorial PORSEC 2010
Radiative flux through the top of the atmosphere Variability in solar radiation reaching the earth Impact of atmospheric constituents
Radiative flux at the planet’s surface Passage through the atmosphere, and emission by the
atmosphere Direct vs. Diffusive Radiation Reflectivity and Albedo
Net energy budget.
Components of ‘Net’ radiative transfer Long wave (terrestrial) vs. Short wave (solar) Upwelling vs. downwelling
Variations in solar incidence angle on the Earth
Radiation Tutorial PORSEC 201012
Incoming Solar Radiation at the Top of the Atmosphere
Radiation Tutorial PORSEC 2010
Solar irradiance on a horizontal surface outside the Earth’s atmosphere [W m-2] from Smithsonian Meteorology Tables (1966). The values are 24 hour means – why do I say this?
Function of Latitude and season Distance from the sun
(season) Tilt of the surface
(season and latitude) Value of solar radiative
flux density, at the mean orbit of the Earth is ~1365 W m-2
Graphic from A First Course in Atmospheric Radiation by G. W. Petty
Radiation Tutorial PORSEC 201014
Meteosat 8
Radiation Tutorial PORSEC 201015
Geostationary satellite developed by ESA and
EUMETSAT. Spectral radiometer,
SEVIRI, will provide data from the surface and the atmosphere every 15 min
Carries a "global"radiation sensor, GERB
A high-tech operational satellite, the new modus
operandi.
Geostationary satellite observing method in early days
Radiation Tutorial PORSEC 201016
Radiation Tutorial PORSEC 201017
Example of new result:
SW↓ (Wm-2) from Meteosat-7 at 0.50, 1 Sep 05, 2005 12 UTC.
Radiation Tutorial PORSEC 201018
Polar orbiting satellites
Radiation Tutorial PORSEC 201019
Both geostationary and polar orbiting satellites are needed for adequate sampling of the diurnal cycle (geostationary) and the polar regions, which are only observed by the polar orbiting satllites.
Radiation Tutorial PORSEC 201020
Surface
Top of Atmosphere
QSW QSW
QSW QSW
Illustration of shortwave radiative fluxesRadiation Tutorial PORSEC 201021
Radiation Tutorial PORSEC 201022
Radiation Tutorial PORSEC 201023
EQuation for surface Net radiation
Q net = SW down + SW up + LW down + LW up
Q net is the sum of the radiative streams at the sea surface SW down is the radiative flux reaching the surface after all the interactions in the atmosphere, it is a fraction of the radiative flux that is downward directed at the top of the atmosphere, TOA. This fraction is called transmittance, T. We know the downward flux at TOA, because we can calculate the solar radiative flux reaching the Earth and we measure the reflected amount. The fraction of reflected radiation is called the albedo.
The earth’s albedo is due to reflection by clouds (dependent on optical thickness), scattering by aerosols, and atmospheric molecules, water vapor and ozone in addition to oxygen and nitrogen. Thus, it depends on composition of the atmosphere and must be measured since this varies.The next slide illustrates these processes, but see also encyclopedia article by Pinker,2005.
Radiation Tutorial PORSEC 201024
Solar radiation budget
Radiation Tutorial PORSEC 2010
• Radiation can be either– Transmitted
• directly or indirectly
– Reflected• Perhaps many
times.• Afterwards returning
to space
– Absorbed• Later reemitted • As infrared or longer
radiationi
Tropopause
Graphic from Meteorology by Danielson, Levin and Abrams
Satellite Estimates of Reflected Solar Radiation
Radiation Tutorial PORSEC 2010
General MeteorologyEnergy Budget 26
Reflected Solar Radiation, May 25, 2000, from the CERES instrument on the TERRA Satellite (scale from 0 to 300 Wm-2).
http://svs.gsfc.nasa.gov/vis/a000000/a002300/a002328/
Why does this pattern occur?
Global Radiation Data SetsGlobal Radiation Data Setsfrom ISCCP, from ISCCP, International Satllite Cloud International Satllite Cloud
Climatolgy ProjectClimatolgy Project
D1 and DX
C1 and C2
1983 1985 1987 1989 1991 1993 1995 1997 1998 2000 2002 2004 2005
Global scale satellite estimates of radiative fluxesAvailable from severalgroups forabout twenty years at spatial resolution of 0.5-2.50; temporal of 3-hours to monthly UMD/SRB at 0.50 resolution
Radiation Tutorial PORSEC 2010
27
Radiation ProjectsInternational SatelliteCloud Climatology Project, ISCCP Surface Radiation Budget (SRB) Project (Global)• Global Water Vapor Project GPVP• Global Precipitation Climatology Project (GPCP)• Global Aerosol Climatology Project GACP Baseline Surface RaadiationNetwork,BSRN
Global Energy and Water Cycle Experiment
Radiation Tutorial PORSEC 2010
28
Radiation Tutorial PORSEC 201029
Radiation Tutorial PORSEC 201030
Radiation Tutorial PORSEC 201031
Model Estimates and Calibration
Radiation Tutorial PORSEC 201032
• Flux estimates are based on radiative transfer calculations using input data from satellite observations on 1) top of the atmosphere reflected shortwave,— converted to clear sky vs. cloudy regions, merged with information about aerosols, surface albedo2) outgoing longwave, converted to SST…3) Calibration against surface measurements on buoys or ships (and ground stations on land)
Summary of the processing sequence to infer surface radiative fluxes. (after Pinker, Encyclopedia chapter)
Radiation Tutorial PORSEC 201033
Photosynthetically Active Radiation, PAR.
Carbon Cycle - PAR affects carbon uptake by ecosystems; carbon
uptake by plants is enhanced when diffuse component of PAR is enhanced.
Estimation of evaporative flux from vegetation
Affects stomatal resistance
Application Areas Agricultural productivity,, Ecological Forecasting, Oceanic
Productivity (Nutrients +sunshine+phytoplankton=growth)
Radiation Tutorial PORSEC 201034
Multi-institutional GEWEX Continental Scale
International Project (GCIP) and GEWEX Americas Prediction Project (GAPP)
Surface Radiation Budget (SRB) Data
Produced in real time at NOAA at 0.5 deg; distributed bythe U of MD at: http://www.atmos.umd.edu/~srb/ Parameters provided: short-wave and PAR (global and diffuse); TOP net; cloud amount; cloud optical depth; surface skin tempGCIP/GAPP: Special Issue JGR -2004
Radiation Tutorial PORSEC 201035
Radiation Tutorial PORSEC 2010
36
How Good are Buoy Observations?• Tropical Atmosphere Ocean (TAO)
Triangle Trans-Ocean Buoy Network (TRITON) Array: 33 buoys
• Pilot Research Moored Array in the Atlantic (PIRATA): 10 buoys
• Baseline Surface Radiation Network (BSRN): 18 sites over land
• Time period: January 1, 2003-December 31, 2005
• A study conducted at U of Maryland with MODIS-observations and buoys
Radiation Tutorial PORSEC 201037
Daily mean surface SW flux estimated by UMD/SRB_MODIS against PIRATA buoys January 1, 2003-December 31, 2005. Cases eliminated: 1.1% Radiation Tutorial PORSEC
201038
Radiation Tutorial PORSEC 201039
For METEOSAT-8 cloud optical parameters provided by R. Hollmann, CMSAFRadiation Tutorial PORSEC 201040
UMD/SRB CCSM3-NCAR
UKMO-HadGEM1 CNR-CM3-Meteo France
DISRIBUTION OF SW↓ OVER TROPICAL PACIFIC AMIP II Models versus Satellite Estimates
Rodriguez-Puebla, Pinker, and Nigam, 2008. Ann. Geophys., 26. Radiation Tutorial PORSEC 201041
Active research concerns Aerosol properties
Radiation Tutorial PORSEC 201042
Modelling of radiative effects of aerosol content giving‘climatological’ aerosol properties are used as ‘default’ inputs to the radiative transfer model to this day BUT…
New satellite systems allow direct real time measurements of the outgoing radiation from aerosol species. This should improve accuracy in time.
Difference in daily average SW↓ W/m-2 July 1, 2004 with and without “Merged” -default aerosols
Radiation Tutorial PORSEC 2010
43
Terrestrial Radiation
Radiation Tutorial PORSEC 2010General MeteorologyEnergy Budget 44
If a radiometer (set for the IR band) was pointed up from the surface, it would measure the temperature of emitters (mostly water related): Cloud bottoms Cloud sides Clear sky, which includes atmospheric gas- emissions
(3-molecule gases, H2O, CO2,O3).
● Terrestrial radiation from sea and much of land surfaces, , is related to radiative flux of a black body. It can be approximated as being emitted in portion to the fourth power of the temperature of the surface of that body in degrees Kelvin.LW up= ε T4, where is the Stephan-Boltzmann constant
= 5.67 x 108 Wm-2K-4, and ε is the emissivityClouds can reasonably be approximated as gray bodies,
with 90 to 95% the irradiance of a black body. This percentage is called the emissivity
(). Most Earth surfaces are not perfect black bodies. Emissivity of the ocean is about 0.98, but depends somewhat on sea state.
This image is provided by the Japan Meteorological Agency (JMA)and brought to you by the National Oceanic and Atmospheric Administration (NOAA). To learn more about their data, go to the JMA /MTSAT site Infrared image, Nov 23, 2008, 22:30 Z
Radiation Tutorial PORSEC 201045
Satellite-based Longwave Radiation Emission Into Space
Radiation Tutorial PORSEC 2010
• Satellites can measure the outgoing longwave radiation (OLR).
• Given enough satellites in reasonable orbits, an average can be determined.
• This example is for January, averaged over several years.
• Units are Wm-2
What does this picture appear to tell you?
Graphic from Meteorology by Danielson, Levin and Abrams
Energy Budget
Radiation Tutorial PORSEC 2010
General MeteorologyEnergy Budget 47
• On average 99 of the 105 units emitted from the surface are absorbed in the atmosphere; 6 of the 105 units escape to space.
This will vary regionally and depend on the local weather.
• WE NEED SEA SURFACE TEMPERATURE, SST, TO CALCULATE LW UP
• Cloud cover is the key factor. Recall that water is a great absorber of IR radiation.
Graphic from Meteorology by Danielson, Levin and Abrams
Mean Downward Longwave flux
Radiation Tutorial PORSEC 201048
Downward Longwave Radiation
Radiation Tutorial PORSEC 201049
Radiation Tutorial PORSEC 201050
Daily OI Analysis for Sea Surface Temperature
Richard W. Reynolds (NOAA, NCDC) Thomas M. Smith (NOAA, STAR)Chunying Liu (NOAA, NCDC)Dudley B. Chelton (Oregon State University)Kenneth S. Casey (NOAA, NODC)Michael G. Schlax (Oregon State University)
SST Analysis
Radiation Tutorial PORSEC 201051
Higher temporal and spatial resolution usually improve SST analyses
Resolution due to many factors including
Grid resolution Spatial & temporal error correlation scales Data and analysis errors Input data resolution Preliminary data screening (QC = Quality
Control) First guess estimates
Analysis error estimates must be improved
Users must be careful!
Top: AVHRR Pathfinder Bottom: AMSR-E
For AVHRR:• Absolute latitudes > 40° have
roughly only 5 days of data
• Number of days increases toward the tropics
• Drop offs due to cloud cover
For AMSR:• Absolute latitudes > 40° have
more than 20 days of data
• Drop offs due to precipitation in ITCZ and SPCZ
Radiation Tutorial PORSEC 201052
Jan '03: Number of Days with Nighttime
Obs
52
SST EXAMPLE from Meteosat 8
Radiation Tutorial PORSEC 201053
Concept Map: Mean Global Energy Budget
Radiation Tutorial PORSEC 2010
TOADown
100 SolarUp
30 Solar70 LW
AtmosphereAbsorbed
20 Solar99 LW6 Sensible24 Latent
Emitted149 LW
SurfaceAbsorbed
50 Solar85 LW
Emitted105 LW6 Sensible24 Latent
The net flux through every layer is zero. This is true only as a long term, global average (assuming no global change).
Graphic from Meteorology by Danielson, Levin and Abrams
Averages of January, February, March, 1996 (W m-2)
Radiation Tutorial PORSEC 201055
Sensible Heat Flux from IFREMER (Oct’96 –August ’97)
Radiation Tutorial PORSEC 201056
Summary
Radiation Tutorial PORSEC 201057
• The radiative fluxes are fundamental in evaluating the climatic patterns of air-sea energy transfer. The main heat balance is between shortwave absorbed and latent heat loss. Oceanic currents and atmospheric weather systems distribute excess heat from tropics to higher latitudes.
• New satellite systems allow increased accuracy and better sampling. Much more is to com
• GOOD LUCK TO YOU WITH YOUR SCIENTIFIC WORK!
Radiation Tutorial PORSEC 201058
A few more References
Rossow W.B. and Schiffer R.A.1991: ISCCP cloud data products. Bulletin of the American Metorological Society, 72(1), 2-20Rossow W.B. and Schiffer R.A.1999: Advances in understanding clouds from ISCCP. Bulletin of the American Metorological Society, 80(11)2261-2287.
Radiation Tutorial PORSEC 201059