Add support for basic filter operations
Closed this issue · 9 comments
This issue has two components:
- code to calculate filter-weighted integrals and
- data files with tabulated filter curves.
Existing python implementations of the code are in:
Filter curves are collected in several places:
- desisim/data/
- desimodel/data/throughput/
- idlutils/data/filters/ (last updated in 2002)
- kcorrect/data/filters
This issue is to implement the code in the same style as other speclite methods, so that others can try it out and give feedback, and to collect a basic set of filter curves sufficient for doing work now (SDSS, DES, LSST, WISE, UVB ?)
@moustakas Anything to add to this?
There's also some filter code in
- desispec.fluxcalibration
- desispec.io.filters
Other than that, this issue has been well-described. Thanks.
I don't know -- this pre-dates me. Mike Blanton and @djschlegel would presumably know.
Here is a graph of the r-band curves from these two sources:
@djschlegel pointed me to more recent work in arxiv:1002.3701 and recommended that we use, so that is now the plan. Specifically, we will adopt the average (over camcols 1-6) reference responses of Table 4, which include an assumed airmass 1.3 APO atmosphere (as was also the case for the 2001 curves).
I got the average response curves from Doi (which are not available online, but he plans to fix this). The next question is what format they should be stored in:
- Binary vs ASCII: I vote for ASCII since it is human readable and the values are relatively low precision (so portability of machine-precision values is not an issue).
- How to capture table and column metadata in a standard way? This astropy note has a nice comparison of the existing ASCII options and opted for a new ECSV format.
Here is an example ECSV format header:
# %ECSV 0.9
# ---
# datatype:
# - {name: wavelength, unit: Angstrom, datatype: float64}
# - {name: response, datatype: float64}
# meta: !!omap
# - {url: 'http://dx.doi.org/10.1088/0004-6256/139/4/1628'}
# - {band: u}
# - {airmass: 1.3}
# - {description: 'SDSS 2.5m telescope reference u-band response function at adopted
# 1.3 airmass APO atmospheric transmission.
#
# Values are the product of the u and atmospheric transmission columns from Table
# 4 of:
#
# Doi et al, "Photometric Response Functions of the SDSS Imager",
#
# The Astronomical Journal, Volume 139, Issue 4, pp. 1628-1648 (2010).
#
# All response values outside the wavelength range covered here are zero.'}
wavelength response
2930.0 0.0
2940.0 0.0001
2960.0 0.0003
2980.0 0.0005
...
Whatever the format, these files are small enough to keep in the repo under speclite/data/filters/.
@moustakas @sbailey @weaverba137 Comments / opinions?
I agree ASCII and the ECSV format looks fine/great.
Sounds good to me, especially since speclite is already astropy-affiliated (or at least going down that path).