Custom sensors

Sensor collects radiance with a certain spectral sampling interval (SSI) and defined spectral response function (SRF). In the simples case SRF is just a gaussian curve with the centre at the band wavelength and width defined with full width half maximum (FWHM).

We convolve irradiance from atmfile (resolution 0.01 nm) (or Esun, Esky (resolution 1 nm)) and simulated reflected radiance to the sensor parameters.

Hyperspectral

Out of the box hyperspectral sensors are:

  1. ASD

  2. HyPlant2018

  3. FLOX_SPEC2

  4. A sensor with constant FWHM over whole measurement wavelength

Hyperspectral instruments typically have individual sensors for visible and SWIR regions with different FWHM. However, taken that SSI is < 3 nm and FWHM is relatively small, we do not think it is necessary to reconstruct the gaussian curve for each spectral region.

../_images/FWHM.png

From this figure you can see that FWHM is important for accurate radiance simulation, but not so important for reflectance.

Multispectral

Out of the box multispectral sensors are:

  1. Sentinel-3:

    • S3A_OLCI

    • SLSTR

  2. Sentinel-2:

    • MSI

Warning

After adding SRF of sensor to input/sensors.xlsx add its name into io.read_fixed_input() (line 22)

+io/read_fixed_input.m
16    %% collect
17
18    fixed.spectral = spectral;
19    fixed.pcf = pcf;
20    fixed.optipar = optipar.optipar;
21    fixed.srf_sensors = {'S3A_OLCI', 'MSI', 'YOUR_NEW_SENSOR_NAME_AS_SHEET_NAME_IN_SENSORS_XLSX'};
22end

For satellites SRFs are known and can be added in input/sensors.xlsx.

For other multispectral sensors we recommend reconstructing the SRF as a gaussian curve from FWHM with helpers.create_sensor_from_fwhm(input_path)().

input_path - path to an excel file with sheet ‘fwhm’ with two columns - band centre, fwhm.

The function will write the second sheet ‘sensor’ that can be copied to input/sensors.xlsx. The function will also plot the resulting SRFs.

The example of input_path is in input/bands_from_fwhm.xlsx.

Note

Having introduced new sensor, you might want to perform a sensitivity analysis with Synthetic data generation to find out which parameters can be retrieved with your sensor.