CLASSI Spectrograph Instrument Simulator

Detector, instrument, throughput, and WCS models for the MLO CLASSI spectrograph.

Install

Install the shared data package first when developing from sibling checkouts:

python -m pip install -e ../shared-data
python -m pip install -e .

The distribution is named classi-sim; its import namespace is simulator:

from simulator import InstrumentSimulator, SpectrographModel

Physical hardware models live in simulator.components. The component catalog keeps hardware geometry and calibration-data associations together so the simulator and ETC can use the same definitions. For example:

from astropy import units as u
from simulator import AtmosphericExtinction, InstrumentSimulator, SpectrographModel
from simulator.components import (
    CANON_EF100_F2,
    CLASSI_FIBER,
    DESI_SKY_DARK,
    CLAUD_50INCH,
    E02_PICKOFF,
    FGL400S,
    FLI_AR571,
    NEWPORT_MASTER_1294,
    THORLABS_AC508_180_AB,
)

spectrograph = SpectrographModel.from_components(
    detector=FLI_AR571,
    grating=NEWPORT_MASTER_1294,
    collimator=THORLABS_AC508_180_AB,
    camera_lens=CANON_EF100_F2,
    fiber=CLASSI_FIBER,
    incidence_angle=32 * u.deg,
    diffraction_angle=-20 * u.deg,
    fiber_count=7,
    fiber_pitch=250 * u.um,
    optical_elements=(E02_PICKOFF, FGL400S),
)

sim = InstrumentSimulator(
    spectrograph=spectrograph,
    telescope=CLAUD_50INCH,
    atmosphere=AtmosphericExtinction(airmass=1.3),
    sky=DESI_SKY_DARK,
    binning=2,
)

The simulator exposes its detector readout wavelength calibration as a specreduce.wavesol1d.WavelengthSolution1D object:

solution = sim.wavelength_solution
wavelength = solution.pix_to_wav(pixel) * solution.unit
pixel = solution.wav_to_pix(wavelength.to_value(solution.unit))

SpectrographModel.wavelength_solution describes the native detector grid, while InstrumentSimulator.wavelength_solution describes the configured readout grid after binning. The x_to_wavelength() and wavelength_to_x() methods delegate to these solutions.

When the spectrograph is constructed from components, the simulator obtains the fiber, collimator, grating, camera lens, camera window, and detector QE throughput curves directly from those components. CLASSI_FIBER carries the installed 10-m fiber length used for its attenuation curve. Additional passive optics such as the pickoff mirror and order-blocking filter are attached once through optical_elements.

DESI dark, grey, and bright sky spectra are provided by shared_data and are treated as at-observatory surface brightnesses. The simulator scales them by the circular fiber sky area and applies downstream instrument throughput, but does not apply atmospheric extinction to them a second time.

Detector definitions describe the native physical sensor. Readout binning is selected per simulator instance with binning=1, 2, 4, etc. The optical signal, dark current, saturation, and read noise are evaluated on the native pixels before square bins are summed. Gain and the output bias are then applied to the binned image. sim.readout describes the output detector grid, and sim.readout_spectrograph provides wavelength/pixel geometry in that binned coordinate system.

The existing numeric SpectrographModel(...) constructor remains available for custom geometries and backward compatibility.