IKONOS

[This page is under construction]

IKONOS is a commercial earth observation satellite. Details about the sensor are provided at Digital Globe's IKONOS Data Sheet

Availability (Sample Data)

• Search for commercial satellite image providers in the internet.
• The Global Land Cover Facility (GLCF) provides four openly available IKONOS scenes of western Sichuan.
• ISPRS provides a small IKONOS data set, fragments from a Panchromatic image as well as from a Stereo product.

Pre-Processing Overview

Typically, multispectral satellite data are converted into physical quantities such as Radiance or Reflectance before they are subjected in multispectral analysis techniques (image interpretation, band arithmetic, vegetation indices, matrix transformations, etc.). The latter can be differentiated in Top of Atmosphere Reflectance (ToAR) which does not account for atmospheric effects (absorption or scattering) and in Top of Canopy Reflectance (ToCR) which introduces a "correction" for atmospheric effects.

In order to derive Reflectance values, likewise as with remotely sensed data acquired by other sensors, IKONOS raw image digital numbers (DNs) need to be converted to at-sensor spectral Radiance values. At-sensor spectral Radiance values are an important input for the equation to derive Reflectance values. Note, Spectal Radiance is the measure of the quantity of radiation that hits the sensor and typically expressed in Failed to parse (syntax error): {\displaystyle W * sr^−1 * m^−2 * nm^−1} , that is watts per unit source area, per unit solid angle, and per unit wavelength.

Converting DNs to at-sensor Radiance can be done by using the following equation:

$L\lambda ={\frac {10^{4}*DN\lambda }{CalCoef\lambda *Bandwidth\lambda }}$

Converting to Top of Atmosphere Reflectance, also referred to as Planetary Reflectance, can be done by using the following equation:

Failed to parse (syntax error): {\displaystyle \rho_p = \frac{\pi * L\lambda * d^2}{ESUN\lambda * cos(θ_S)}}

where:

• $\rho$ - Unitless Planetary Reflectance
• $\pi$ - mathematical constant (3.14159265358)
• $L\lambda$ spectral Radiance at the sensor's aperture, from equation... ToADD
• $d$ - Earth-Sun distance in astronomical units, interpolated values
• $Esun$ - Mean solar exoatmospheric irradiance(s) (W/m2/μm), interpolated values
• Failed to parse (syntax error): {\displaystyle cos(θ_s)} - Solar zenith angle, from the image acquisition's metadata

Modules overview

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Pre-Processing

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File Formats & Metadata

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Importing data

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Calculate Planetary Reflectance

Converting a Blue Band (Digital Numbers) in to Spectral at-sensor Radiance in the correct units to be further used for the conversion in to unitless Reflectance:

r.mapcalc "Blue_Radiance = ( (10000 * IKONOS_Blue_Band_DN) / (728 * 71.3) )"

Converting the in-Blue spectral band at-sensor Radiance in to Planerary Reflectance:

r.mapcalc "Blue_Reflectance = ( ${PI} * Blue_Radiance * ${ESD}^2 ) / ( ${!BAND_Esun} * cos(${SZA}) )"

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Atmospheric correction

See Atmospheric correction

Color composites

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Pan Sharpening

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IKONOS Image classification

See Image classification

References / Sources

• http://www.apollomapping.com/wp-content/user_uploads/2011/09/IKONOS_Esun_Calculations.pdf
• http://web.unicen.edu.ar/crecic/docs/radrefl.pdf
• Some short presentation about the DN to Reflectance conevrsion: Calibrated Landsat Digital Number (DN) to Top of Atmosphere (TOA) Reflectance Conversion, by Richard Irish

See also

• GRASS-Wiki page about Image Processing

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