Helper methods¶

The SixSHelpers module contains a number of helper functions that improve the ease-of-use of Py6S. These include functions to set 6S parameters from various external data sources, as well as functions to make it easy to produce wavelength and BRDF plots from 6S runs.

Running for many wavelengths¶

The Wavelengths class contains functions to run 6S over a number of wavelength ranges.

For example, the following code runs 6S simulations across the Visible-Near Infrared wavelength range and plots the results, producing the output shown below:

from Py6S import *
s = SixS()
s.aero_profile = AeroProfile.PredefinedType(AeroProfile.Maritime)
wavelengths, values = SixSHelpers.Wavelengths.run_vnir(s, output_name='pixel_radiance')
SixSHelpers.Wavelengths.plot_wavelengths(wavelengths, values, 'Pixel Radiance (W/m^2)')

A similar function exist to run across the whole 6S wavelength range (run_whole_range()), and arbritary lists of wavelengths can be run using the run_wavelengths() function. For example, you can manually specify a number of wavelengths to run for:

wv, res = SixSHelpers.Wavelengths.run_wavelengths(s, [0.46, 0.67, 0.98], output_name='apparent_radiance')

If you want to run user-specific ranges of wavelengths then you can use the handy numpy functions arange and linspace to generate the lists of wavelengths for you. For example:

# Run the model between 0.5 and 0.7um with a step of 0.001um (1nm)
wv, res = SixSHelpers.Wavelengths.run_wavelengths(s, np.arange(0.5, 0.7, 0.001), output_name='apparent_radiance')

# Run the model at 50 equally-spaced wavelengths in the range 0.9-1.5um
wv, res = SixSHelpers.Wavelengths.run_wavelengths(s, np.linspace(0.9, 1.5, 50), output_name='apparent_radiance')

Functions also exist to run for all bands of the various sensors supported in 6S (for example, run_landsat_tm(), run_modis() and run_aatsr()). It should be noted that for these functions, bands which are outside of the 6S wavelength range (0.2-4.0um), such as the Landsat thermal band, will not be simulated. The example below shows the creation of a plot for the Landsat ETM bands:

from Py6S import *
s = SixS()
s.aero_profile = AeroProfile.PredefinedType(AeroProfile.Maritime)
wavelengths, values = SixSHelpers.Wavelengths.run_landsat_etm(s, output_name='pixel_reflectance')
SixSHelpers.Wavelengths.plot_wavelengths(wavelengths, values, 'Pixel Reflectance')

The supported sensors are:

Landsat MSS, TM and ETM

SPOT HRV1, HRV2 and Vegetation

MERIS

MODIS

POLDER

SeaWiFS

AATSR

ASTER

VIIRS

ER2 MODIS Airborne Simulator (MAS)

ALI

GLI

class Py6S.SixSHelpers.Wavelengths[source]¶

Helper functions for running the 6S model for a range of wavelengths, and plotting the result

classmethod run_wavelengths(s, wavelengths, output_name=None, n=None, verbose=False)[source]¶

Runs the given SixS parameterisation for each of the wavelengths given, optionally extracting a specific output.

This function is used by all of the other wavelengths running functions, such as :method:`run_vnir`, and thus any arguments that are passed to this function can also be passed to these other functions.

The calls to 6S for each wavelength will be run in parallel, making this function far faster than simply running a for loop over each wavelength.

Arguments:

s – A SixS instance with the parameters set as required
wavelengths – An iterable containing the wavelengths to iterate over
output_name – (Optional) The output to extract from s.outputs, as a string that could be placed after s.outputs., for example pixel_reflectance
n – (Optional) The number of threads to run in parallel. This defaults to the number of CPU cores in your system, and is unlikely to need changing.
verbose – (Optional) Print wavelengths as Py6S is running (default=False)

Return value:

A tuple containing the wavelengths used for the run and the results of the simulations. The results will be a list of SixS.Outputs instances if output_name is not set, or a list of values of the selected output if output_name is set.

Example usage:

# Run for all wavelengths from 0.4 to 0.5 micrometers, with a spacing of 1nm, returns SixS.Outputs instances
wavelengths, results = SixSHelpers.PredefinedWavelengths.run_wavelengths(s, np.arange(0.400, 0.500, 0.001))
# Run for all wavelengths from 0.4 to 0.5 micrometers, with a spacing of 1nm, returns a list of pixel radiance values
wavelengths, results = SixSHelpers.PredefinedWavelengths.run_wavelengths(s, np.arange(0.400, 0.500, 0.001), output_name='pixel_radiance')
# Run for the first three Landsat TM bands
wavelengths, results = SixSHelpers.PredefinedWavelengths.run_wavelengths(s, [PredefinedWavelengths.LANDSAT_TM_B1, PredefinedWavelengths.LANDSAT_TM_B2, PredefinedWavelengths.LANDSAT_TM_B3)

classmethod run_vnir(s, spacing=0.005, **kwargs)[source]¶

Runs the given SixS parameterisation for wavelengths over the Visible-Near Infrared range, optionally extracting a specific output.

By default, the given model is run for wavelengths from 0.4-1.4um, with a spacing of 5nm.

Arguments:

s – A SixS instance with the parameters set as required
spacing – (Optional) The spacing to use between each wavelength, in um. Eg. a spacing of 0.001 is a spacing of 1nm.
output_name – (Optional) The output to extract from s.outputs, as a string that could be placed after s.outputs., for example pixel_reflectance

Return value:

A tuple containing the wavelengths used for the run and the results of the simulations. The results will be a list of SixS.Outputs instances if output_name is not set, or a list of values of the selected output if output_name is set.

Example usage:

# Run for the VNIR wavelengths, with the default spacing (5nm), returning SixS.Outputs instances
wavelengths, results = SixSHelpers.PredefinedWavelengths.run_vnir(s)
# Run for the VNIR wavelengths, with a spacing of 10nm, returning pixel reflectance values
wavelengths, results = SixSHelpers.PredefinedWavelengths.run_vnir(s, spacing=0.010, output_name='pixel_reflectance')

classmethod run_whole_range(s, spacing=0.01, **kwargs)[source]¶

Runs the given SixS parameterisation for the entire wavelength range of the 6S model, optionally extracting a specific output.

By default, the given model is run for wavelengths from 0.2-4.0um, with a spacing of 10nm.

Arguments:

s – A SixS instance with the parameters set as required
spacing – (Optional) The spacing to use between each wavelength, in um. Eg. a spacing of 0.001 is a spacing of 1nm.
output_name – (Optional) The output to extract from s.outputs, as a string that could be placed after s.outputs., for example pixel_reflectance

Return value:

A tuple containing the wavelengths used for the run and the results of the simulations. The results will be a list of SixS.Outputs instances if output_name is not set, or a list of values of the selected output if output_name is set.

Example usage:

# Run for the VNIR wavelengths, with the default spacing (5nm), returning SixS.Outputs instances
wavelengths, results = SixSHelpers.PredefinedWavelengths.run_vnir(s)
# Run for the VNIR wavelengths, with a spacing of 10nm, returning pixel reflectance values
wavelengths, results = SixSHelpers.PredefinedWavelengths.run_vnir(s, spacing=0.010, output_name='pixel_reflectance')

classmethod to_centre_wavelengths(item)[source]¶

Get centre wavelengths for a sensor from a list of the wavelength tuples.

This is calculated simple as minwv+((maxwv-minwv)/2) and is the CENTER wavelength (that is the wavelength in the middle of the range) not necessarily the peak wavelength.

classmethod run_landsat_tm(s, **kwargs)[source]¶

Runs the given SixS parameterisation for all of the Landsat TM bands within the 6S band range, optionally extracting a specific output.

Arguments:

s – A SixS instance with the parameters set as required
output_name – (Optional) The output to extract from s.outputs, as a string that could be placed after s.outputs., for example pixel_reflectance

Return value: