# Glossary

:::{glossary}
:sorted: true

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:
  $\text{airmass} = 1 / \sin(\text{elevation})$.

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: $f_{amb} = 1 - f_{eff}$.

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 $T_A^*$ 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
  $b(\nu)$ and $c(\nu)$ 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.

DBS

: Dual beam switch -- OTF-chopped observing mode where the telescope
  alternates between two beam positions (A and B) during scanning.

SKYDIFF

: Diagnostic mode that differences consecutive SKY (OFF) observations
  with a hot-load RJ correction, revealing instrumental drifts and
  standing waves.

gain interpolation

: Correction for receiver gain drift between two bracketing HOT/COLD
  calibration scans. Level 2 corrects ON counts; level 3 corrects
  ON+OFF counts.

provenance

: Metadata tracking the processing chain from L2 output back to L0
  source data, including calibration scan numbers and processing
  parameters.

linked PWV

: Multi-frontend PWV pooling: for observations with multiple
  frontends (e.g., HFA + LFA), PWV estimates are pooled across all
  frontends for physically consistent atmospheric correction.

zenith opacity

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