Digital Image Processing: A Remote Sensing
Perspective
FW5560
Lecture 6
Radiometric Correction
Radiometric correction
Improving the accuracy of surface spectral reflectance or
emittance. Would like to obtain measurements of absolute
reflectance or emittance at the earth’s surface. Must consider
contributions and subtraction imposed by atmospheric
components.
Also consider gains and bias of the sensors themselves.
Electromagnetic
Spectrum
Concept of R adiant Flux Density
Radiant flux,
Irradiance

E =
 
Area, A
Radiant flux,
Exitance

M =
 
Area, A
Radiant Flux Density
The concept of radiant flux
density for an area on the
surface of the earth.
Irradiance (E) is a measure
of the amount of incoming
energy in Watts m-2.
Exitance (M) is a measure of
the amount of energy leaving
in Watts m-2.
Radiance (L) is the radiant flux per unit solid angle leaving an
extended source in a given direction per unit projected source area
in that direction and is measured in watts per meter squared per
steradian (W m-2 sr -1 ). We are only interested in the radiant flux in
certain wavelengths (L) leaving the projected source area (A)
within a certain direction () and solid angle ():


L
cos
This is the most precise remote
sensing radiometric measurement.
Concept of Radiance
Norm al
t o Surface
Radiant flux,

Side view
of Source
Area, A
Solid Angle,


L
 A Cos
Project ed Source Area =A Cos
Various Path s of
Sate l li te Re ce ive d Radiance
Tot al radiance
L
at t he sensor S
Remote
sensor
det ector
Sol ar
E
irradi ance 0
Lp
90Þ
T
LT
The total radiance reaching
the sensor is:
0
T
2
Diffuse sky
irradi ance E d
Energy-matter Interactions in
the Atmosphere, at the Study
Area, and at the Remote
Sensor Detector
1
1,3,5
4
v
Atmosphere
v
3
0
LI
5
Reflect ance from Reflect ance from
nei ghboring area,
study area,
rn
r
1
LS    T v EoT o cos  o   Ed   L p

Primary Focal Plane (PFP), where
the silicon detectors for bands 1-4
and 8 are located. A portion of the
scene energy is redirected from the
PFP to the Cold Focal Plane where
the detectors for bands 5, 7, and 6
are located. The spectral filters for
the bands are located directly in
front of the detectors.
Landsat 7 Handbook
The Landsat 7 ETM+ instrument achieves its 185-kilometer
cross-track ground swath by using a bi-directional scan mirror to
traverse the instrument line-of-sight through a 15-degree crosstrack field of view. On descending passes, the mirror alternately
scans west-to-east (forward scan) and then east-to-west (reverse
scan). The active Earth-imaging portion of each scan lasts for,
nominally, 60.743 milliseconds. During this time, the Landsat 7
spacecraft advances approximately 410 meters downtrack.
An estimated 22 percent of any
given scene is lost because of the
SLC failure. The maximum width
of the data gaps along the edge of
the image would be equivalent to
one full scan line, or approximately
390 to 450 meters. The precise
location of the missing scan lines
will vary from scene to scene.
Gap Mask Legend Values:
green = primary scene
blue = fill scene 1
yellow = fill scene 2
pink = fill scene 3
red = no data (not filled)
Band-specific gap mask files
are included with every Scan
Line Corrector (SLC)-off
Level 1 Terrain (L1T)
corrected standard product.
These ancillary data allow
you to identify the location
of all pixels affected by the
original data gaps in the
primary SLC-off scene.
The gap mask is provided as
a series of individual band
files, in compressed (GZIP)
GeoTIFF format.