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


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



Graphic of ocean’s role in Climate

Illustration of air-sea interactions

Radiation Tutorial PORSEC 20106Bourassa 08 /

Electromagentic spectrum


Components of Net Radiative Transfer


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

Considerations in the Radiative Budget


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


Incoming Solar Radiation at the Top of the Atmosphere


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

Meteosat 8


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


Example of new result:

SW↓ (Wm-2) from Meteosat-7 at 0.50, 1 Sep 05, 2005 12 UTC.


Polar orbiting satellites


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.

Surface

Top of Atmosphere

QSW QSW

QSW QSW

Illustration of shortwave radiative fluxesRadiation Tutorial PORSEC 201021

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.


Solar radiation budget


• 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


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


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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


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Model Estimates and Calibration


• 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)


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)


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



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


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

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


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


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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


Satellite-based Longwave Radiation Emission Into Space


• 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?


Energy Budget


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.


Mean Downward Longwave flux


Downward Longwave Radiation



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


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


Jan '03: Number of Days with Nighttime

Obs

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SST EXAMPLE from Meteosat 8


Concept Map: Mean Global Energy Budget


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).


Averages of January, February, March, 1996 (W m-2)


Sensible Heat Flux from IFREMER (Oct’96 –August ’97)


Summary


• 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!

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 and remote sensing radiation tutorial porsec 2010 1 tutorial lecture in keelung, taiwan,...

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