========
Glossary
========

.. glossary::
   :sorted:

   T_A*
      Antenna temperature corrected for atmospheric absorption (K).
      The primary output of the calibration engine.

   gamma
      Gain calibration factor converting count differences to temperature
      differences (K/count).

   T_rec
      Receiver noise temperature. ``T_rec_prime`` is the double-sideband
      value; ``T_rec_SSB`` is the single-sideband value.

   T_sys
      System temperature — total noise contribution including receiver,
      atmosphere, and load coupling (K).

   PWV
      Precipitable water vapour — column-integrated water vapour along
      the zenith line of sight (mm).

   airmass
      Atmospheric path length relative to zenith:
      :math:`\text{airmass} = 1 / \sin(\text{elevation})`.

   foeff
      Forward efficiency — fraction of the beam that terminates on the
      sky (as opposed to ambient spillover). Typically 0.95–0.99.

   f_amb
      Ambient coupling fraction: :math:`f_{amb} = 1 - f_{eff}`.

   g_s x_s
      Signal sideband gain × suppression product. For an ideal DSB
      receiver: 0.5.

   g_i x_i
      Image sideband gain × suppression product. For an ideal DSB
      receiver: 0.5.

   OTF
      On-the-fly mapping — the telescope scans continuously across the
      source, recording multiple dumps per subscan.

   TP
      Total power — position-switched observation with discrete ON/OFF
      pointings.

   L0
      Raw data level — uncalibrated counts and metadata in Zarr format.
      Produced by zarr-fits-core from FITS files.

   L1
      Calibrated data level — antenna temperature :math:`T_A^*` spectra,
      system temperature, flags, and quality metrics.

   L1b
      Reduced data level — baseline-subtracted, flagged, and quality-
      checked spectra. Produced by the reduction pipeline.

   L2
      Science-ready data level — gridded spectral maps. Produced by the
      reduction pipeline.

   ATM table
      Precomputed atmospheric model providing opacity coefficients
      :math:`b(\nu)` and :math:`c(\nu)` as a function of frequency and
      pressure. Produced by atmospheric radiative transfer codes.

   HOT load
      Ambient-temperature blackbody calibration source (~300 K).

   COLD load
      Cryogenic calibration source, typically liquid nitrogen (~77 K).

   sobsmode
      Subscan observing mode string (ON, OFF, OTF-ON, OTF-OFF, HOT,
      COLD, COL, SKY, ZERO).

   dump
      A single time integration sample within a subscan.

   subscan
      One continuous observing phase (e.g., one ON pointing or one OTF
      scan leg) within a scan.

   scan
      A complete observation unit containing source subscans and
      associated calibration data.

   SSB
      Single-sideband — calibration convention where the atmospheric
      correction is applied to the signal sideband only.

   DSB
      Double-sideband — both signal and image sidebands contribute
      to the detected power.

   Zarr v3
      Chunked array storage format used for all data levels. Supports
      zstd compression and vlen-utf8 strings.

   zenith opacity
      Optical depth along the zenith direction:
      :math:`\tau_0 = b(\nu) \cdot \text{PWV} + c(\nu)`.