- Summary
Record of simulated exposures.
- Naming Convention
exposures_surveysim.fits- Regex
exposures_surveysim\.fits- File Type
FITS, 2 MB (scales with the number of exposures)
Note: currently this is only an output from surveysim, but it may become an output of survey operations, caching in a file the information that is also contained in the operations database.
| Number | EXTNAME | Type | Contents |
|---|---|---|---|
| HDU0 | META | IMAGE | Blank |
| HDU1 | EXPOSURES | BINTABLE | Per-exposure metadata |
| HDU2 | TILEDATA | BINTABLE | Per-tile metadata |
EXTNAME = META
| KEY | Example Value | Type | Comment |
|---|---|---|---|
| TILES | desi--tiles.fits | str | Name of the tiles file specified in desisurvey config. |
| NEXP | 41875 | int | Number of exposures recorded so far. |
| INITIAL | 2019-12-01 | str | YEAR-MM-DD of initial night used for integer offsets (or blank before any observing). |
Empty HDU.
EXTNAME = EXPOSURES
Per-exposure metadata.
| KEY | Example Value | Type | Comment |
|---|---|---|---|
| NAXIS1 | 41875 | int | length of dimension 1 |
| NAXIS2 | 8 | int | length of dimension 2 |
| Name | Type | Units | Description |
|---|---|---|---|
| MJD | float64 | MJD when shutter was opened for this exposure. | |
EXPTIME TILEID SNR2FRAC AIRMASS |
float32 int32 float32 float32 |
s |
Length of time shutter was open. ID of the observed tile. Fractional SNR2 accumulated on this tile during this exposure. Average airmass during this exposure. |
SEEING TRANSP SKY |
float32 float32 float32 |
arcsec |
Average FWHM atmospheric seeing during this exposure. Average atmospheric transparency during this exposure. Average sky background level during this exposure. |
EXTNAME = TILEDATA
Per-tile metadata.
| KEY | Example Value | Type | Comment |
|---|---|---|---|
| NAXIS1 | 20 | int | length of dimension 1 |
| NAXIS2 | 10 | int | length of dimension 2 |
| Name | Type | Units | Description |
|---|---|---|---|
AVAIL PLANNED |
int32 int32 |
Night when this tile was first available (or -1 if not yet available). Night when this tile was first planned (or -1 if not yet planned). |
|
EXPTIME SNR2FRAC NEXP |
float32 float32 int32 |
s |
Total exposure time of this tile. Total fractional SNR2 accumulated on this tile. Total number of exposures of this tile. |
There is one table row per tile, indexed to match desisurvey.tiles.Tiles.
The integer AVAIL and PLANNED values are nights since the date specified by the NIGHT keyword in HDU0.
A tile is considered "available" once it has fibers assigned. A tile is considered "planned" once its priority has been set non-zero. In general, these changes of state occur independently: availability is determined by the fiber assignment policy and when covering tiles have been completed, while the priorities are set by survey strategy rules. A tile will not be scheduled until it is both available and planned.
An ExposuresList object records exposures during simulation:
import surveysim.exposures
explist = surveysim.exposures.ExposureList()Its internal state after a simulation (or each night) can be saved using, for example:
explist.save('exposures.fits', comment='Baseline (seed=1)')This state can then later be restored using:
explist = surveysim.exposures.ExposureList(restore='exposures.fits')