# The `pyspectral` API¶

pyspectral.blackbody.blackbody(wavel, temp)

Derive the Planck radiation as a function of wavelength.

SI units. blackbody(wavelength, temperature) wavel = Wavelength or a sequence of wavelengths (m) temp = Temperature (scalar) or a sequence of temperatures (K)

Output: The spectral radiance per meter (not micron!)

Unit = W/m^2 sr^-1 m^-1

Derive brightness temperatures from radiance using the Planck function.

Wavelength space. Assumes SI units as input and returns temperature in Kelvin

pyspectral.blackbody.blackbody_wn(wavenumber, temp)

Derive the Planck radiation as a function of wavenumber.

SI units. blackbody_wn(wavnum, temperature) wavenumber = A wavenumber (scalar) or a sequence of wave numbers (m-1) temp = A temperatfure (scalar) or a sequence of temperatures (K)

per m-1: Unit = W/m^2 sr^-1 (m^-1)^-1 = W/m sr^-1

Converting from SI units to mW/m^2 sr^-1 (cm^-1)^-1: 1.0 W/m^2 sr^-1 (m^-1)^-1 = 1.0e5 mW/m^2 sr^-1 (cm^-1)^-1

Derive brightness temperatures from radiance using the Planck function.

Wavenumber space

pyspectral.blackbody.planck(wave, temperature, wavelength=True)

Derive the Planck radiation as a function of wavelength or wavenumber.

SI units. _planck(wave, temperature, wavelength=True) wave = Wavelength/wavenumber or a sequence of wavelengths/wavenumbers (m or m^-1) temp = Temperature (scalar) or a sequence of temperatures (K)

Output: Wavelength space: The spectral radiance per meter (not micron!)

Unit = W/m^2 sr^-1 m^-1

Wavenumber space: The spectral radiance in Watts per square meter per steradian per m-1: Unit = W/m^2 sr^-1 (m^-1)^-1 = W/m sr^-1

Converting from SI units to mW/m^2 sr^-1 (cm^-1)^-1: 1.0 W/m^2 sr^-1 (m^-1)^-1 = 1.0e5 mW/m^2 sr^-1 (cm^-1)^-1

## Spectral responses¶

Reading the spectral responses in the internal pyspectral hdf5 format.

Bases: `object`

Data container for the Relative Spectral Responses for all (supported) satellite sensors.

property rsr_data_version_uptodate

Check whether RSR data are up to date.

Bases: `dict`

Helper dict-like class to handle multiple names for band keys.

Container for the relative spectral response functions for various satellite imagers.

convert()

Convert spectral response functions from wavelength to wavenumber.

get_bandname_from_wavelength(wavelength, epsilon=0.1, multiple_bands=False)

Get the band name from the wavelength.

get_number_of_detectors4bandname(h5f, bandname)

For a band name get the number of detectors, if any.

get_relative_spectral_responses(h5f)

integral(bandname)

Calculate the integral of the spectral response function for each detector.

Read the internally formatet hdf5 relative spectral response data.

set_band_central_wavelength_per_detector(h5f, bandname, detector_name)

Set the central wavelength for the band and detector.

set_band_names(h5f)

Set the band names.

set_band_responses_per_detector(h5f, bandname, detector_name)

Set the RSR responses for the band and detector.

set_band_wavelengths_per_detector(h5f, bandname, detector_name)

Set the RSR wavelengths for the band and detector.

set_description(h5f)

Set the description.

set_instrument(h5f)

Set the instrument name.

set_platform_name(h5f)

Set the platform name.

Base class for reading raw instrument spectral responses.

Bases: `object`

Base class for the raw (agency dependent) instrument response functions.

Module to read solar irradiance spectra and calculate the solar flux over various instrument bands given their relative spectral response functions

Bases: `object`

Total Top of Atmosphere (TOA) Solar Irradiance Spectrum.

Wavelength is in units of microns (10^-6 m). The spectral Irradiance in the file TOTAL_IRRADIANCE_SPECTRUM_2000ASTM is in units of W/m^2/micron

convert2wavenumber()

Convert from wavelengths to wavenumber.

Units:

Wavelength: micro meters (1e-6 m) Wavenumber: cm-1

inband_solarflux(rsr, scale=1.0, **options)

Get the in band solar flux.

Derive the inband solar flux for a given instrument relative spectral response valid for an earth-sun distance of one AU.

Get the in band solar irradiance.

Derive the inband solar irradiance for a given instrument relative spectral response valid for an earth-sun distance of one AU.

(Same as the in band solar flux).

interpolate(**options)

Interpolate Irradiance to a specified evenly spaced resolution/grid.

This is necessary to make integration and folding (with a channel relative spectral response) straightforward.

dlambda = wavelength interval in microns start = Start of the wavelength interval (left/lower) end = End of the wavelength interval (right/upper end) options: dlambda: Delta wavelength used when interpolating/resampling ival_wavelength: Tuple. The start and end interval in wavelength space, defining where to integrate/convolute the spectral response curve on the spectral irradiance data.

plot(plotname=None, **options)

Plot the data.

solar_constant()

Calculate the solar constant.

## Near-Infrared reflectance¶

Derive NIR reflectances of a a band in the 3-4 micron window region.

Derive the Near-Infrared reflectance of a given band in the solar and thermal range (usually the 3.7-3.9 micron band) using a thermal atmospheric window channel (usually around 11-12 microns).

class pyspectral.near_infrared_reflectance.Calculator(platform_name, instrument, band, detector='det-1', wavespace='wavelength', solar_flux=None, sunz_threshold=85.0, masking_limit=85.0)

Bases: `RadTbConverter`

A thermal near-infrared (~3.7 micron) band reflectance calculator.

Given the relative spectral response of the NIR band, the solar zenith angle, and the brightness temperatures of the NIR and the Thermal bands, derive the solar reflectance for the NIR band removing the thermal (terrestrial) part. The in-band solar flux over the NIR band is optional. If not provided, it will be calculated here!

The relfectance calculated is without units and should be between 0 and 1.

Derive the CO2 correction to be applied to the 3.9 channel.

Derive the 3.9 radiance correction factor to account for the attenuation of the emitted 3.9 radiance by CO2 absorption. Requires the 11 micron window band and the 13.4 CO2 absorption band, as e.g. available on SEVIRI. Currently only supports the Rosenfeld method

emissive_part_3x(tb=True)

Get the emissive part of the 3.x band.

reflectance_from_tbs(sun_zenith, tb_near_ir, tb_thermal, **kwargs)

Derive reflectances from Tb’s in the 3.x band.

The relfectance calculated is without units and should be between 0 and 1.

Inputs:

sun_zenith: Sun zenith angle for every pixel - in degrees

tb_near_ir: The 3.7 (or 3.9 or equivalent) IR Tb’s at every pixel

(Kelvin)

tb_thermal: The 10.8 (or 11 or 12 or equivalent) IR Tb’s at every

pixel (Kelvin)

tb_ir_co2: The 13.4 micron channel (or similar - co2 absorption band)

brightness temperatures at every pixel. If None, no CO2 absorption correction will be applied.

pyspectral.near_infrared_reflectance.get_as_array(variable)

Return variable as a Dask or Numpy array.

Variable may be a scalar, a list or a Numpy/Dask array.

## Rayleigh scattering¶

Atmospheric correction of shortwave imager bands in the wavelength range 400 to 800 nm.

class pyspectral.rayleigh.Rayleigh(platform_name, sensor, **kwargs)

Container for the atmospheric correction of satellite imager bands.

This class removes background contributions of Rayleigh scattering of molecules and Mie scattering and absorption by aerosols.

get_reflectance(sun_zenith, sat_zenith, azidiff, band_name_or_wavelength, redband=None)

Get the reflectance from the three sun-sat angles.

static reduce_rayleigh_highzenith(zenith, rayref, thresh_zen, maxzen, strength)

Reduce the Rayleigh correction amount at high zenith angles.

This linearly scales the Rayleigh reflectance, rayref, for solar or satellite zenith angles, zenith, above a threshold angle, thresh_zen. Between thresh_zen and maxzen the Rayleigh reflectance will be linearly scaled, from one at thresh_zen to zero at maxzen.

class pyspectral.rayleigh.RayleighConfigBaseClass(aerosol_type, atm_type='us-standard')

Bases: `object`

A base class for the Atmospheric correction, handling the configuration and LUT download.

property lutfiles_version_uptodate

Tell whether LUT file is up to date or not.

Do a check for the version of the atmospheric correction LUTs and attempt downloading only if needed.

pyspectral.rayleigh.get_reflectance_lut_from_file(lut_filename)

Get reflectance LUT.

Read the Look-Up Tables from file with reflectances as a function of wavelength, satellite zenith secant, azimuth difference angle, and sun zenith secant.

## Utils¶

Utility functions.

pyspectral.utils.AEROSOL_TYPES = ['antarctic_aerosol', 'continental_average_aerosol', 'continental_clean_aerosol', 'continental_polluted_aerosol', 'desert_aerosol', 'marine_clean_aerosol', 'marine_polluted_aerosol', 'marine_tropical_aerosol', 'rayleigh_only', 'rural_aerosol', 'urban_aerosol']

class pyspectral.utils.NullHandler(level=0)

Bases: `Handler`

Empty handler.

emit(record)

Record a message.

pyspectral.utils.are_instruments_identical(name1, name2)

Given two instrument names check if they are both describing the same instrument.

Takes care of the case of AVHRR where the internal pyspectral naming (following WMO Oscar) is is with a slash as in ‘avhrr/1’, but where a naming using a dash instead is equally accepted, as in ‘avhrr-1’.

pyspectral.utils.bytes2string(var)

Decode a bytes variable and return a string.

Check instrument name and try fix if inconsistent.

It checks against the possible listed instrument names for each platform. It also makes an adjustment replacing names like avhrr/1 with avhrr1, removing the ‘/’.

pyspectral.utils.convert2hdf5(ClassIn, platform_name, bandnames, scale=1e-06, detectors=None)

Retrieve original RSR data and convert to internal hdf5 format.

scale is the number which has to be multiplied to the wavelength data in order to get it in the SI unit meter

pyspectral.utils.convert2str(value)

Convert a value to string.

Parameters

value – Either a str, bytes or 1-element numpy array

pyspectral.utils.convert2wavenumber(rsr)

Convert Spectral Responses from wavelength to wavenumber space.

Take rsr data set with all channels and detectors for an instrument each with a set of wavelengths and normalised responses and convert to wavenumbers and responses

Rsr

Relative Spectral Response function (all bands)

Returns

retv: Relative Spectral Responses in wave number space :info: Dictionary with scale (to go convert to SI units) and unit

pyspectral.utils.debug_on()

Turn debugging logging on.

See `pyspectral.rayleigh.check_and_download()` for a “smart” version of this process that only downloads the necessary files.

Parameters
• aerosol_types (Iterable) – Aerosol types to download the LUTs for. Defaults to all aerosol types. See `AEROSOL_TYPES` for the full list.

• aerosol_type (str) – Deprecated.

Download the pre-compiled HDF5 formatted relative spectral response functions from the internet as tarballs, extracts them, then deletes the tarball.

See `pyspectral.rsr_reader.check_and_download()` for a “smart” version of this process that only downloads the necessary files.

Parameters
• dest_dir (str) – Path to put the temporary tarball and extracted RSR files.

pyspectral.utils.get_bandname_from_wavelength(sensor, wavelength, rsr, epsilon=0.1, multiple_bands=False)

Get the bandname from h5 rsr provided the approximate wavelength.

pyspectral.utils.get_central_wave(wav, resp, weight=1.0)

Calculate the central wavelength or the central wavenumber.

Calculate the central wavelength or the central wavenumber, depending on which parameters is input. On default the weighting funcion is f(lambda)=1.0, but it is possible to add a custom weight, e.g. f(lambda) = 1./lambda**4 for Rayleigh scattering calculations

pyspectral.utils.get_logger(name)

Return logger with null handle.

pyspectral.utils.get_rayleigh_lut_dir(aerosol_type)

Get the rayleigh LUT directory for the specified aerosol type.

pyspectral.utils.get_wave_range(in_chan, threshold=0.15)

Return central, min and max wavelength in an RSR greater than threshold.

An RSR function will generally start near zero, increase to a maximum and then drop back to near zero. This function takes advantage of this to find the first and last points where the RSR is greater than a threshold. These points are then defined as the minimum and maximum wavelengths for a given channel, and can be used, for example, in Satpy reader YAML files.

pyspectral.utils.logging_off()

Turn logging off.

pyspectral.utils.logging_on(level=30)

Turn logging on.

pyspectral.utils.np2str(value)

Convert an numpy.string_ to str.

Parameters

value (ndarray) – scalar or 1-element numpy array to convert

Raises

ValueError – if value is array larger than 1-element or it is not of type numpy.string_ or it is not a numpy array

pyspectral.utils.sort_data(x_vals, y_vals)

Sort the data so that x is monotonically increasing and contains no duplicates.