Glossary

airmass

: Atmospheric path length relative to zenith:

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

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.

DBS

: Dual beam switch – OTF-chopped observing mode where the telescope

alternates between two beam positions (A and B) during scanning.

DSB

: Double-sideband — both signal and image sidebands contribute

to the detected power.

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.

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.

foeff

: Forward efficiency — fraction of the beam that terminates on the

sky (as opposed to ambient spillover). Typically 0.95–0.99.

g_i x_i

: Image sideband gain × suppression product. For an ideal DSB

receiver: 0.5.

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.

gamma

: Gain calibration factor converting count differences to temperature

differences (K/count).

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).

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.

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.

OTF

: On-the-fly mapping — the telescope scans continuously across the

source, recording multiple dumps per subscan.

provenance

: Metadata tracking the processing chain from L2 output back to L0

source data, including calibration scan numbers and processing parameters.

PWV

: Precipitable water vapour — column-integrated water vapour along

the zenith line of sight (mm).

scan

: A complete observation unit containing source subscans and

associated calibration data.

SKYDIFF

: Diagnostic mode that differences consecutive SKY (OFF) observations

with a hot-load RJ correction, revealing instrumental drifts and standing waves.

SSB

: Single-sideband — calibration convention where the atmospheric

correction is applied to the signal sideband only.

T_A*

: Antenna temperature corrected for atmospheric absorption (K).

The primary output of the calibration engine.

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).

TP

: Total power — position-switched observation with discrete ON/OFF

pointings.

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:

$\tau_0 = b(\nu) \cdot \text{PWV} + c(\nu)$.