radiance2Reflectance

Convert radiance to reflectance

Syntax

newhcube = radiance2Reflectance(hcube)

newhcube = radiance2Reflectance(hcube,'BlockSize',blocksize)

Description

newhcube = radiance2Reflectance(hcube) converts the pixel values of the hyperspectral data cube from radiance to reflectance values. The function returns a new hypercube object and the pixel values of the data cube represent the top of atmosphere (TOA) reflectance. For more information, see TOA Reflectance.

newhcube = radiance2Reflectance(hcube,'BlockSize',blocksize) specifies the block size for block processing of the hyperspectral data cube by using the name-value pair argument 'BlockSize'.

The function divides the input image into distinct blocks, processes each block, and then concatenates the processed output of each block to form the output matrix. Hyperspectral images are multi-dimensional data sets that can be too large to fit in system memory in their entirety. This can cause the system to run out of memory while running the radiance2Reflectance function. If you encounter such an issue, perform block processing by using this syntax.

For example, radiance2Reflectance(hcube,'BlockSize',[50 50]) divides the input image into non-overlapping blocks of size 50-by-50 and then computes the reflectance values for pixels in each block.

Note

To perform block processing by specifying the 'BlockSize' name-value pair argument, you must have MATLAB R2021a or a later release.

Note

This function requires the Image Processing Toolbox™ Hyperspectral Imaging Library. You can install the Image Processing Toolbox Hyperspectral Imaging Library from Add-On Explorer. For more information about installing add-ons, see Get and Manage Add-Ons.

Examples

Convert Radiance to Reflectance Values

Read hyperspectral data into the workspace.

input = hypercube('EO1H0440342002212110PY_cropped.hdr');

Determine the bad spectral band numbers using the BadBands parameter in the metadata.

bandNumber = find(~input.Metadata.BadBands);

Remove the bad spectral bands from the data cube.

input = removeBands(input,'BandNumber',bandNumber);

Convert the digital numbers to radiance values by using the dn2radiance function.

hcube = dn2radiance(input);

Convert the radiance values to reflectance values by using the radiance2Reflectance function.

newhcube = radiance2Reflectance(hcube);

Read and display the 80th spectral band in the input radiance and the output reflectance data.

radianceBand = hcube.DataCube;
reflectanceBand = newhcube.DataCube;
band = 80;

figure
subplot(1,2,1)
imagesc(radianceBand(:,:,band))
axis off
title('Radiance Band')
subplot(1,2,2)
imagesc(reflectanceBand(:,:,band))
title('Reflectance Band')

colormap(gray)
axis off    

Input Arguments

hcube — Input hyperspectral data

hypercube object

Input hyperspectral data, specified as a hypercube object. The DataCube property of the hypercube object stores the hyperspectral data cube. The pixels values of the data cube must be radiance values specifying the amount of radiation from the surface being imaged. You can convert the pixel values in digital numbers to radiance values by using dn2radiance function.

blocksize — Size of data blocks

2-element vector of positive integers

Size of the data blocks, specified as a 2-element vector of positive integers. The elements of the vector correspond to the number of rows and columns in each block, respectively. The size of the data blocks must be less than the size of the input image. Dividing the hyperspectral images into smaller blocks enables you process large data sets without running out of memory.

• If the blocksize value is too small, the memory usage of the function reduces at the cost of increased execution time.

• If the blocksize value is large or equal to the input image size, the execution time reduces at the cost of increased memory usage.

Example: 'BlockSize',[20 20] specifies the size of each data block as 20-by-20.

Output Arguments

newhcube — Output hyperspectral data

hypercube object

Output hyperspectral data, returned as a hypercube object. The pixels values in the output data cube are top of atmosphere (TOA) reflectance values.

More About

TOA Reflectance

The TOA reflectance values specifies the ratio of radiation reflected by the surface to the radiation incident on the surface.

$$\text{Reflectance }{\rho }_{\lambda }=\frac{\pi d^2{L}_{\lambda }}{ESU{N}_{\lambda }{\theta }_E}$$

d is the earth-sun distance in astronomical units, ESUN_λ is the mean solar irradiance for each spectral band, and θ_E is the sun elevation angle.

L_λ is the spectral radiance computed as:

$${\text{Radiance L}}_{\lambda }=\left(DN\times Gain\right)+Bias$$

Gain and Bias are the gain and offset values for each spectral bands respectively. The Metadata property of hypercube object contains the gain and offset values.