Glossary

Terms from radio astronomy, air-shower physics and RF engineering that appear in field names, arguments and these pages.

10-second trigger: A trigger that records the units every ten seconds whatever the signal, to measure the background. trigger_pattern_10s marks its events.
ADC: Analogue-to-digital converter. In GRAND, 14 bits over a 1.8 V full scale, giving a quantization step of 109.9 µV. Also the name of the tree that stores what a unit actually recorded, TADC.
ADF: Angular distribution function: a model of the radio amplitude around the shower axis. grand.analysis fits it to the units’ amplitudes to estimate the energy. Its results are the *_adf fields of TRecons.
analysis level: How far a file has been processed, written into the file name as _L0_ or _L1_ and into the tree as analysis_level. In a simulation, level 0 is the simulator’s electric field and the voltages computed from it. Level 1 is what the detector would record: the ADC counts, plus an electric field filtered, resampled and given noise. See The data model.
arm: One of the three antenna elements of a detection unit: X (south-north), Y (east-west) and Z (vertical). A voltage trace has one row per arm. An arm is not a component of the electric field.
balun: Balanced-to-unbalanced transformer. Converts between the antenna’s balanced feed and the unbalanced coaxial line. Two appear in the RF chain, one after the low-noise amplifier and one before the ADC.
channel: One of the four inputs of a unit’s ADC, 0 to 3, as in TADC.trace_ch. Voltages and electric fields have arms or components, not channels.
DC2: The second GRAND Data Challenge: a collaboration-wide exercise in which a common simulated dataset is produced and analyzed.
DU: Detection unit, or unit for short. One antenna with its three arms, its electronics and its digitizer. du_id identifies it; du_xyz is its position in the array frame. Antenna in these pages means the antenna itself, not the whole unit.
ECEF: Earth-centered, Earth-fixed. A Cartesian frame with its origin at the center of the Earth, rotating with it. GRANDlib uses it as the pivot through which all other frame conversions pass; see Coordinates and conventions.
effective length: The vector \(\boldsymbol{\ell}(\nu, \theta, \phi)\) that gives an antenna arm’s response to an incoming field: \(V_{\mathrm{oc}} = \boldsymbol{\ell}\cdot\boldsymbol{E}\). Complex, so the antenna disperses as well as scales. Notebook 03.
ellipsoidal height: Height above the WGS-84 reference ellipsoid, which is what GPS reports and what Geodetic stores. Not the same as height above sea level; see geoid undulation.
geoid undulation: The difference between the ellipsoidal height and height above mean sea level, reaching ±100 m worldwide and −61 m at the GRANDProto300 site. Notebook 07.
GP13: A thirteen-unit GRAND prototype array. Appears as a du_type and in several file names.
GP300: GRANDProto300: the 300-unit prototype array at Dunhuang, China and the default du_type throughout the simulation.
GP80: A GRAND prototype array of about 80 units, which took data in 2025. Its files are named GP80_...; see Working with measured data.
GRANDCS: The GRAND coordinate system: a local Cartesian frame with x pointing north, y west and z up. Distinct from LTP with orientation='ENU', where x is east. Getting these two confused rotates a layout by 90°.
gtot: The collaboration’s converter from the binary files the detectors write to ROOT files in GRANDlib’s format. It is not part of GRANDlib.
GULL: The geomagnetic-field library GRANDlib compiles from source, wrapping IGRF and WMM. Built by src/Makefile.
Handling3dTraces: The in-memory container for a set of three-arm traces, in grand.basis.traces_event, with plotting and peak-finding methods.
LFMap: A low-frequency sky map of Galactic brightness temperature. Folded through the antenna response, it is the source of the Galactic-noise tables; notebook 05.
LNA: Low-noise amplifier. The first active stage of the RF chain and the one that sets the receiver noise figure.
LST: Local sidereal time, in hours. The Galactic-noise level is tabulated against it, because the Galactic plane rises and sets on a sidereal day.
LTP: Local Tangent Plane. A Cartesian frame tangent to the ellipsoid at a chosen origin, with a selectable orientation such as 'ENU' or 'NWU'.
NUTRIG: The GRAND online trigger project. The nutrig_* fields of TADC carry correlation quantities produced by it.
open-circuit voltage: \(V_{\mathrm{oc}}\), the voltage at the antenna terminals before any electronics. The output of the antenna stage and the input to the RF chain.
PWF: Plane-wave fit: the arrival direction from the times at which the pulse reaches each unit, for a flat wave front. Its results are the *_pwf fields of TRecons.
RF chain: The cascade of two-port networks between the antenna and the ADC: matching network, LNA, baluns, cable and a variable-gain amplifier with a filter. Notebook 04.
S-parameters: Scattering parameters, what a vector network analyser measures. They do not cascade by multiplication, which is why GRANDlib converts each stage to an ABCD matrix first.
sim2root: The tools that convert ZHAireS or CoREAS output into the GRAND format. They live in sim2root/; see Converting simulations: sim2root.
SRTM: Shuttle Radar Topography Mission. The elevation dataset TURTLE reads, shipped as one .hgt file per one-degree square. Not in version control.
SWF: Spherical-wave fit: like the PWF, for a curved wave front, which also gives the distance to where the emission comes from, near Xmax. Its results are the *_swf fields of TRecons.
T1: The first-level trigger: each unit decides from its own trace whether to record an event. t1_du_triggers() applies an offline version to ADC traces.
TRecons: The tree that stores reconstruction results: for each event, the direction, the distance to the emission and the energy estimate.
TTree: A ROOT data structure: a table whose columns (branches) can hold variable-length arrays. Everything GRAND records or simulates lives in one.
TURTLE: The topography library GRANDlib compiles from source, which reads SRTM tiles and performs ray–ground intersection.
VGA: Variable-gain amplifier. Its setting is exposed as vga_gain and is currently ignored.
Xmax: The atmospheric depth at which an air shower reaches its maximum number of particles, in g/cm². xmax_pos_shc is the corresponding position, expressed in the shower-core frame.
ZHAireS: One of the two air-shower simulation codes GRAND uses upstream; CoREAS is the other. Neither is part of GRANDlib.