exposures¶
- 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.
Contents¶
Number |
EXTNAME |
Type |
Contents |
|---|---|---|---|
META |
IMAGE |
Blank |
|
EXPOSURES |
BINTABLE |
Per-exposure metadata |
|
TILEDATA |
BINTABLE |
Per-tile metadata |
FITS Header Units¶
HDU0¶
EXTNAME = META
Required Header Keywords¶
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.
HDU1¶
EXTNAME = EXPOSURES
Per-exposure metadata.
Required Header Keywords¶
KEY |
Example Value |
Type |
Comment |
|---|---|---|---|
NAXIS1 |
41875 |
int |
length of dimension 1 |
NAXIS2 |
8 |
int |
length of dimension 2 |
Required Data Table Columns¶
Name |
Type |
Units |
Description |
|---|---|---|---|
MJD |
float64 |
MJD when shutter was opened for this exposure. |
|
EXPTIME |
float32 |
s |
Length of time shutter was open. |
TILEID |
int32 |
ID of the observed tile. |
|
SNR2FRAC |
float32 |
Fractional SNR2 accumulated on this tile during this exposure. |
|
AIRMASS |
float32 |
Average airmass during this exposure. |
|
SEEING |
float32 |
arcsec |
Average FWHM atmospheric seeing during this exposure. |
TRANSP |
float32 |
Average atmospheric transparency during this exposure. |
|
SKY |
float32 |
Average sky background level during this exposure. |
HDU2¶
EXTNAME = TILEDATA
Per-tile metadata.
Required Header Keywords¶
KEY |
Example Value |
Type |
Comment |
|---|---|---|---|
NAXIS1 |
20 |
int |
length of dimension 1 |
NAXIS2 |
10 |
int |
length of dimension 2 |
Required Data Table Columns¶
Name |
Type |
Units |
Description |
|---|---|---|---|
AVAIL |
int32 |
Night when this tile was first available (or -1 if not yet available). |
|
PLANNED |
int32 |
Night when this tile was first planned (or -1 if not yet planned). |
|
EXPTIME |
float32 |
s |
Total exposure time of this tile. |
SNR2FRAC |
float32 |
Total fractional SNR2 accumulated on this tile. |
|
NEXP |
int32 |
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.
Notes and Examples¶
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')