LSF effect description for mode lms_cube

METIS/METIS_LMS_SMPL.yaml

@@ -13,6 +13,7 @@ properties:
   pixel_scale: 0.0082          # arcsec / pixel
   plate_scale: 0.455555555556  # arcsec / mm
   fp2_platescale: 0.303        # arcsec / mm
+  slice_width: 0.0207          # arcsec / slice
   decouple_detector_from_sky_headers: True  # needed for spectroscopy
   flatten: False  # cube output
 
@@ -38,6 +39,17 @@ effects:
       wave_key: "WAVELENG"
       bkg_width: -1
 
+  - name: lsf
+    description: line-spread function for spectroscopic domain
+    class: LineSpreadFunction
+    kwargs:
+      wavelen: "!OBS.wavelen"
+      fit_slope:      3.795e-06  # use to compute dlam_per_pix [um/pix] as
+      fit_intercept: -4.659e-07  #   a function of wavelength [um]
+      slice_width: "!INST.slice_width"
+      pixel_scale: "!INST.pixel_scale"
+      spec_binwidth: "!SIM.spectral.spectral_bin_width"
+
   - name: flux_binning
     description: turn per arcsec per um to ph per s
     class: FluxBinning3D

METIS/code/fit_ifu_dispersion.py

@@ -0,0 +1,46 @@
+"""Compute IFU mean dispersion as a function of central wavelength
+
+The LineSpreadFunction effect needs the dispersion dlam_per_pix on
+the LMS detector to determine the width of the LSF kernel to be
+applied to the cube in mode `lms_cube`. The script computes the mean
+dispersion as (lam_max - lam_min)/4220 for a number of wavelength settings,
+and then performs a linear regression of dlam_per_pix against wavelength.
+LineSpreadFunction() uses the slope and intercept to get a sufficient
+approximation to the dispersion without having to reference TRACE_LMS.fits
+or instantiate MetisLMSSpectralTraces itself.
+"""
+# Author: Oliver Czoske
+# Date:   2025-05-21
+
+import numpy as np
+from scipy.stats import linregress
+from matplotlib import pyplot as plt
+import scopesim as sim
+
+if __name__ == "__main__":
+    sim.link_irdb("../../")    # from METIS/code/
+
+    NPIX = 4220    # twice 2048 plus gap, from FPA_metis_lms_layout.dat
+    wavelens = np.linspace(2.677, 5.332, 100)   # um
+    dlam_per_pix = np.zeros_like(wavelens)
+
+    for i, lamc in enumerate(wavelens):
+        cmd = sim.UserCommands(use_instrument="METIS",
+                               set_modes=["lms"],
+                               properties={"!OBS.wavelen": lamc})
+        metis = sim.OpticalTrain(cmd)
+        splist = metis['lms_spectral_traces']
+        lam_min = splist.meta['wave_min']
+        lam_max = splist.meta['wave_max']
+
+        dlam_per_pix[i] = (lam_max - lam_min) / NPIX
+
+    linfit = linregress(wavelens, dlam_per_pix)
+    slope = linfit.slope
+    intercept = linfit.intercept
+    print("Slope:    ", slope, "# um/pix")
+    print("Intercept:", intercept, "# um")
+
+    plt.plot(wavelens, dlam_per_pix, 'o')
+    plt.plot(wavelens, intercept + slope * wavelens)
+    plt.show()

METIS/default.yaml

@@ -6,7 +6,7 @@ alias: OBS
 name: METIS_default_configuration
 description: default parameters needed for a METIS simulation
 status: development
-needs_scopesim: "0.9"
+needs_scopesim: "v0.9"
 date_modified: 2024-09-04
 changes:
   - 2021-12-16 (OC) chopnod defaults to perpendicular
@@ -366,7 +366,7 @@ mode_yamls:
     name: lms_cube
     description: "METIS LM-band integral-field spectroscopy, nominal mode, cube output"
     status: experimental
-    needs_scopesim: "0.10.0a1"
+    needs_scopesim: "v0.10.0a1"
     yamls:
       - Armazones.yaml
       - ELT.yaml