problem interpolating atmosphere in desisim.specsim.get_simulator about desisim

[moustakas]

This ticket is a bit of a rabbit hole and I'm inclined to close it. The crash actually occurs in specsim when the atmospheric extinction is interpolated onto the input wavelength grid--
https://github.com/desihub/specsim/blob/master/specsim/config.py#L488

However, the extinction grid only extends to 9999.9 A while the wavelength grid in the example in this ticket extends to 10000.0 A and so an extrapolation exception is raised. In its defense, specsim does have some options to allow for extrapolated interpolation, but it looks like some of the options in scipy may have changed since the code was written.

Unfortunately, choosing a shorter maximum wavelength results in a different crash that I'm not inspired to pursue:

from desisim.simexp import simulate_spectra
from desisim.templates import ELG
flux, wave, meta, obj = ELG(maxwave=9990).make_templates(1, seed=1)
sim1 = simulate_spectra(wave, flux)
INFO:io.py:971:read_basis_templates: Reading /Users/ioannis/work/desi/spectro/templates/basis_templates/v3.2/elg_templates_v2.2.fits
INFO:iers.py:82:freeze_iers: Freezing IERS table used by astropy time, coordinates.
DEBUG:simexp.py:418:simulate_spectra: loading specsim desi config desi
DEBUG:simexp.py:422:simulate_spectra: creating specsim desi simulator
Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "/Users/ioannis/code/desihub/desisim/py/desisim/simexp.py", line 423, in simulate_spectra
    desi = desisim.specsim.get_simulator(config, num_fibers=nspec,
  File "/Users/ioannis/code/desihub/desisim/py/desisim/specsim.py", line 52, in get_simulator
    qsim = specsim.simulator.Simulator(config, num_fibers,
  File "/Users/ioannis/code/desihub/specsim/specsim/simulator.py", line 75, in __init__
    self.instrument = specsim.instrument.initialize(config, camera_output)
  File "/Users/ioannis/code/desihub/specsim/specsim/instrument.py", line 622, in initialize
    initialized_cameras.append(specsim.camera.Camera(
  File "/Users/ioannis/code/desihub/specsim/specsim/camera.py", line 145, in __init__
    raise RuntimeError(
RuntimeError: Wavelength grid min does not cover b-camera response.

For the record, this ticket came up as I was trying to understand #563.