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Noise Processing

Noise Processing. Use Dark Current Image to estimate noise covariance. Noise Processing. Compute mean and covariance of noise. Covariance “Image” 224 x 224 scaled for display shows noise relationships between bands and can be used in noise whitening algorithms.

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Noise Processing

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  1. Noise Processing Use Dark Current Image to estimate noise covariance noise processing

  2. Noise Processing • Compute mean and covariance of noise. Covariance “Image” 224 x 224 scaled for display shows noise relationships between bands and can be used in noise whitening algorithms. • The standard deviation of the noise in each channel can be used to generate a signal-to-noise estimate. • In simplest case, can compute mean DN in each band and generate S/N on band-by-band basis for the given image. But this includes atmosphere, illumination, sensor response, etc. noise processing

  3. Noise Covariance Noise covariance typically computed on dark field image σ11 σ12 Σ = σ21 σ22 ....... σnn (DCin - DCi)(DCjn - DCj) N = Σ σij (N - 1) n = 1 noise processing

  4. Noise Processing • It is often more meaningful in terms of data analysis to compute SNR against a reference reflectance level. • First, need to generate a radiance to reflectance calibration for each band using one of the atmospheric correction methods. Then figure out what radiance (signal) would correspond to the reference level for S/N estimates, NASA JPL sites AVIRIS S/N relative to the 50% reflectance target. • Convert DN noise values to radiance using the AVIRIS sensor calibration. • Now we have signal and noise in common units corresponding to SNR for a 50% ground target. noise processing

  5. Noise Processing noise processing

  6. Noise Processing Comment: calibration involves recording DNk at known radiance level (Lk) and DNo dark (L=0). noise processing

  7. Noise Processing So if DN = mL + b + n where DN is recorded count, m and b are gain and bias and n is noise. Then DNo = b + n is the dark current count and if noise has zero mean, then the average dark current image is b. The gain is given as: - DN DN = o m [counts per radiance unit] L k noise processing

  8. Noise Processing • If noi is the standard deviation of the dark noise image in band i expressed in digital counts, then the standard deviation expressed in radiance units is: • If Li.5 is the radiance in the ith band for a 50% reflector then the SNR for a 50% reflecting target is n s = oi i m i L = . 5 i SNR s i noise processing

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