The orbit mode takes its viewing geometry from a
set of HAWC orbit NetCDF files: one file per orbit (roughly one revolution),
giving the satellite position and the tangent-point locations of the ALI
image over time.
Required contents¶
| Name | Kind | Dimensions | Description |
|---|---|---|---|
time | variable | time | Seconds since orbit_epoch |
latitude | variable | time, along, across | Tangent-point latitude [degrees] |
longitude | variable | time, along, across | Tangent-point longitude [degrees], −180–180 or 0–360 |
observer_latitude | variable | time | Satellite latitude [degrees] |
observer_longitude | variable | time | Satellite longitude [degrees] |
observer_altitude | variable | time | Satellite altitude [m] |
start_time | global attribute | — | Start of the orbit, parseable by pandas |
Only along = 0 is used. The tangent point is the single across-track
pixel center_pixel (default 256, the centre of a 512-pixel row).
How files are grouped by day¶
Each file is assigned to the day (counted from orbit_epoch) of its
start_time attribute. A day can therefore map to several files, and an
orbit that crosses midnight belongs to the day it started on. Reading
every file’s start_time can take minutes for a large set, so the index is
cached in out_dir/.orbit_day_index_cache.json and rebuilt automatically
when files are added, removed or modified.
File names¶
The default pattern is orbit_*.nc; change it with orbit_pattern.