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Solar Electromagnetic Radiation
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Solar Electromagnetic Radiation

Jan 04, 2016

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Solar Electromagnetic Radiation. Satellite Remote Sensing—Landsat 7. Sun-synchronous orbit: Satellite always crossed the equator at precisely the same local time. Temporal Resolution. The shortest time needed to repeat a ground track. Spatial Resolution. Landsat. Field of View. 705km. - PowerPoint PPT Presentation
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Page 1: Solar Electromagnetic Radiation

Solar Electromagnetic Radiation

Page 2: Solar Electromagnetic Radiation

Satellite Remote Sensing—Landsat 7

Sun-synchronous orbit:Satellite always crossed the equator at precisely the same local time.

Page 3: Solar Electromagnetic Radiation

Temporal Resolution

The shortest time needed to repeat a ground track

Page 4: Solar Electromagnetic Radiation

Spatial Resolution

185 km

Field of View

175kmscene

Landsat

Satellite ground tra

ck705km

Spatial Resolution

Pixel size=(30x30m)

Page 5: Solar Electromagnetic Radiation

Data transmission to the ground station, allows faster and efficient data delivery to the ground. As the technology advances, the speed to data transmission increased tremendously allowing us to collect more images from space.

Page 6: Solar Electromagnetic Radiation

Radiometric Resolution

The number of levels of DN values is determined by the radiometric resolution of the instrument. For example, 8-bit system can differentiate 256 (0-255) levels of radiance

MinimumIntensity

MaximumIntensity

Dig

ital n

umbe

rs (

DN

)

Radiance intensity0

255 Radiance DN (min=2, max=130 ) [0.0,2.0] 0 (2.0, 2.5] 1 (2.5, 3.0] 2 … … [100.0,100.5] 196 … [129.5,130.0] 255

Page 7: Solar Electromagnetic Radiation

1010 30

25

5

30

10

30 30

1. Space is covered continuously with cells.2. Each cell has one number indicating the amount of energy received from the cell3. The cell is called pixel (picture element)4. The size of the pixel is the spatial resolution

sensor

Digital Images

Page 8: Solar Electromagnetic Radiation

Landsat 7 ETM+ Spectral Bands

The number of bands and the width of spectrum that each sensor covers are referred to spectral resolution

Page 9: Solar Electromagnetic Radiation

1010 30

25

10

30

10

20 15

1010 30

25

5

30

10

30 30

301 40

15

30

30

12

20 40

Multispectral remotely sensed data

Each band will generate a layer of remotely sensed data, usually with the same cell (pixel) size. For Landsat satellite, we will have 6 layers of data corresponding to the 6 bands.

Page 10: Solar Electromagnetic Radiation

Spectral Vegetation IndexSimple Ratio/Normalized Difference Vegetation Index

dNIR

dNIR

RR

RRNDVI

Re

Re

NDVI: [-1.0, 1.0]

The more the leaves of vegetation present, the bigger theContrast in reflectance in the red and near-infrared spectra.

d

NIR

R

RSR

Re

Page 11: Solar Electromagnetic Radiation

Color Arithmetic

red+green=yellowgreen+blue=cyanred+blue=magenta

Page 12: Solar Electromagnetic Radiation

red

blue

green

white

yellow

black

cyan

magenta

Color Space

Page 13: Solar Electromagnetic Radiation

Landsat Images

Landsat 5 TM image on Dec 10,1988 at Shenzhen special econ. zone, China (RGB=432)

Landsat 5 TM image on Dec 30,1995 at Shenzhen special econ. zone, China (RGB=432)

Page 14: Solar Electromagnetic Radiation

DN to Radiance Conversion

MinimumIntensity

MaximumIntensity

DN

L 0

255

Radiance received at satellite has to be converted DN for effective communication. Users often has to convert the DN back to radiance and further calculate surface reflectance.

DNDN

LLLL

max

λminλmaxλminλ

Where Lλ is the radiance received at satellite sensor, Lλmin is the sensor read of radiance when DN is zero. Lλmax is the maximum radiance read from the sensor producing DNmax. Lλmin, Lλmax, DNmax can be found in the header of the image.

DNGBLλ

Page 15: Solar Electromagnetic Radiation

Apparent Reflectance

Total Energy: JoulesEnergy Flux: J/sEnergy Flux Density (irradiance): J/m2/sRadiance: J/m2/s/srSurface energy flux density is the integration of radiance from the entire upper hemisphere (2π solid angle). Assuming Lambertian surface, the total amount of irradiance the surface reflected is πLλ. Thus the percent energy reflected at the surface with a particular wavelength range, reflectance, would be:

)cos( zE

L

Where Eλ is the solar constant within the wavelength range. θz is solar zenith angle. This is called the at satellite reflectance, or apparent reflectance.

Page 16: Solar Electromagnetic Radiation

Surface Reflectance

))cos((

/)(

downzz

vhazesat

EET

TLL

Where Eλ is the solar constant within the wavelength range. θz is solar zenith angle. Edown is the down welling diffuse radiation.

Edown

Lg

Lhaze Lsat=Lg+Lhaze

Tv=exp(-τ/cos(θv))Tz=exp(-τ/cos(θz))τ is atmospheric optical depth. It is composed of two parts: atmospheric molecules and aerosols.

sun sensor

Page 17: Solar Electromagnetic Radiation

Dark Object

Edown

Lg=0

LhazeLsat=Lg+Lhaze

sun sensor

Lsat=Lhaz

Image Histogram:

DN

Freq Can you find the DN for dark object in the histogram?

Page 18: Solar Electromagnetic Radiation

Dark Object Subtraction

DN

Freq

1000

Real histogram often is noisy. Not all pixels with low DN values are valid pixels. One way to avoid this noise is assuming the highest DN with at least 1000 pixel counts on the lower side of the histogram peak has 1% surface reflectance.

/))cos((01.0min downzzhaze EETBDNGL

Page 19: Solar Electromagnetic Radiation

Transmittance

Tv=exp(-τ/cos(θv))Tz=exp(-τ/cos(θz))τ is atmospheric optical depth. It is composed of two parts: atmospheric molecules and aerosols.

)0.000131130.0(1.0 .0085690 -4-2-4

Aerosol optical depth are difficult to get and it varies from time to time and place to place. However, for a high quality satellite image, aerosol optical depth is relatively low. People used to assume Tv and Tz as 1, Song et al. (2001) showed that we should consider Raleigh atmospheric effect.

Page 20: Solar Electromagnetic Radiation

Surface Reflectance

))cos((

/)(

downzz

vhazesat

EET

TLL

Where Eλ is the solar constant within the wavelength range. θz is solar zenith angle. θv is viewing zenith angle. It is 0 for Landsat (nadir view). Edown is the downwelling diffuse radiation. Can be obtained through 6S, an atmospheric radiation transfer model.

Lsat=G*DN+BLhaze=G*DNmin+B-0.1*(TzEλcos(θz)+Edown)Tv=exp(-τ/cos(θv))Tz=exp(-τ/cos(θz))

)0.000131130.0(1.0 .0085690 -4-2-4

Page 21: Solar Electromagnetic Radiation

AVHRR

AVHRR=Advanced Very High Resolution Radiometer

Temporal Resolution: dailySpatial Resolution: 1km at nadirRadiometric Resolution: 8-bitSpectral: 4/5 bands

Page 22: Solar Electromagnetic Radiation

Where Are the Bands Located ?

Page 23: Solar Electromagnetic Radiation

NDVI Change in China from 1982 to 2000NDVI Change in China from 1982 to 2000

Page 24: Solar Electromagnetic Radiation

MODIS (MODerate resolution Imaging Spectroradiometer)

Temporal Resolution: 2 daysSpatial Resolution: 250, 500, 1000Radiometric Resolution: 12-bitSpectral: 36 bands

Page 25: Solar Electromagnetic Radiation

Leaf Area Index

March 24 - April 8, 2000

Page 26: Solar Electromagnetic Radiation

Monitoring forest fire

Pre-forest fire

Post-forest fire

Burned area identified from space

Page 27: Solar Electromagnetic Radiation

Phytoplankton bloom in the Black Sea. MODIS band 1 (red), 4 (green) and 3 (blue)

Page 28: Solar Electromagnetic Radiation

Sea Surface Temperature

Page 29: Solar Electromagnetic Radiation

1997/1998 El Nino

Page 30: Solar Electromagnetic Radiation

Cloud types from MODIS: pink: cold high level snow and ice clouds; neon green: low level water clouds. Different cloud types reflect and emit radiant energy differently.

Page 31: Solar Electromagnetic Radiation

A massive iceberg, one of the largest ever observed, broke off the Ross Ice Shelf near Roosevelt Island in Antarctica in mid-March 2000. This Iceberg is about 40 miles wide and 300 miles long. The break off of such big iceberg may be related to global climate change.