surveying lecture 3

8/7/2019 Surveying Lecture 3

http://slidepdf.com/reader/full/surveying-lecture-3 1/19

CE-419 : Principles of RemoteSensing

Subashisa Dutta

Department of Civil Engineering

IIT Guwahati

Lecture –6: Physical basis of SignaturesRef: George Joseph, Fundamentals of Remote Sensing

Contact email for lecture ppts : [email protected]

mailto:[email protected]

mailto:[email protected]



SIGNATURE

0.4 0.8 1.2 1.6 2.0 2.4

REFLEC

TANCE

(%)

Wave length (m)

WATER (Shallow/Deep)

VEGETATION

SILTY CLAY SOIL

MUCK SOIL

0

20

40

60

80

Signatures could be inferred through:

• Spectral Variation

• Polarisation Change

• Thermal Inertia

• Temporal Variation

Key to feature identification from space imagery depends on the

characteristic changes in the properties of the EM spectrum

reflected/emitted from the target surface – referred ‘signature’

Signatures are not completely

deterministic; they are statistical in

nature with a mean and dispersion

Radiance (mw/cm2 / str/ m)

0

1000

2000

3000

4000

5000

6000

7000

2.79 3.08 3.37 3.66 3.95 4.24 4.53 4.82

F r e q u e n c y

2S Dutta/CE/IITG8/16/2010



Sample field vegetation spectralmeasurement

Field Measurements




Reflectance from a leaf




The spectral response for inorganic materials is

distinct from vegetation types.




• Gradual rise in reflectance with increasing

wavelengths.

• Concrete, light-colored and bright, has higher

% refl than dark asphalt.




• Refl for veg. rises

abruptly at ~0.7 µm,

followed by a gradual

drop at about 1.1 µm.

0.3 - 0.5 µm - most veg. types similar in response

0.5 - 0.6 µm moderate variations

0.7 - 0.9 µm - maximum variability

(optimum discrimination)




• 4 spectral curves

• Variations in depths of absorption bands.




Some crops distinguishable by separations in 0.56 to 0.66 µm interval.




Spectral signature for paddy fields

Paddy Field Crop height measurement

Paddy field with water

background

Spectroradiometer

( 350 –

1050 nm)




Temporal variation of spectral signature of paddyfields

Data source : NRDMS Project,

IIT Guwahati 17S Dutta/CE/IITG8/16/2010



Background effects of vegetation reflectance spectra

• Vegetation cover reflectance : a mixture of reflectance fromthe vegetation, soil ( water) underneath and the shadow.

•

At the low vegetation cover, background reflectance frombare soil dominates

• At the peak vegetation stage, reflectance from vegetation

dominates

• Controlled by direction of the sun rays and view direction




• End of lecture-6


surveying lecture 3

Documents