Design Notes for Bright Object Checking in the VTT Era
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Bright Object Checking
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The process of bright object checking determines which astronomical
objects in a particular celestial area pose risk to the observatory or
the desired science if observed in a particular mode, ie, with a
particular aperture, a set of spectral elements and a given exposure
time.
There are three modes in which we envision bright object checking
being done in support of HST observing:
1) In the VTT
As targets are being tuned, a PI should be aware of which
astronomical objects are potential risks.
2) A PI Analyzing Their Proposal
A PI should check if any exposures in their proposal pose a risk.
The source of the exposure information for a PI is in a local
file.
3) A CS Analyzing PI Proposals
CS's must check if any exposure in a submitted proposal poses a
risk. The source of the exposure information for CS's is in
databases here at STScI.
The Bright Object Checker Engine
--------------------------------
The bright object checker will be implemented as a java object that
has a well defined interface. This interface supports the input of
a celestial area, aperture and spectral elements and returns a list
of astronomical objects and the exposure times at which they will
exceed bright object alert levels.
The bright object checker will be the core engine that supports all
three modes of bright object checking. The current implementation
of this core engine will be a look up table provided by the
Instrument Scientists.
Bright Object Checking in the VTT
---------------------------------
Ideally, the VTT should be able indicate which of all the displayed
objects pose risk to the observatory or to the intended science of
an observation. However, the number of astronomical objects which
potentially pose a risk is large, so that it is only practical to
analyze those close to a given observation pointing.
The VTT will be able to analyze an area around an aperture and
indicate which objects pose risk. The results of the analysis will
be cached so that areas do not have to be re-analyzed and so that
the analysis is preserved when switching between apertures.
Because it is an expensive process, bright object checking may be
turned on or off. When it is turned on, any repositioning of the
aperture will cause any "new" areas to be processed through the
bright object checker engine.
The results of the analysis are displayed by generating new
catalogs in the VTT Catalog Overlay facility. These catalogs
contain those objects which pose risk. Separate catalogs are
generated for each severity level.
The user may set the parameters which control the bright object
checking :
* Size of the celestial area to analyze in terms of percent larger
than the aperture.
* Set of spectral elements to include.
* Exposure time.
Bright Object Checking by PIs on Their Proposals
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A standalone PI tool will used that is similar to the Batch Image
Retriever which uses an input file containing a list of celestial
areas. The bright object checking tool will use a similar input
file that additionally has aperture, spectral element and exposure
time information.
The standalone PI tool will generate a summary report file that,
for each exposure, records the observation parameters and number of
bright object alerts. For each exposure, an alert file is
generated that contains the bright object analysis for each star in
the field of the exposure. The VTT will be able to read alert
files and create associated apertures loaded with the bright object
analysis.
Bright Object Checking by CSs on PI Proposals
---------------------------------------------
A tool similar to the current bright object tool will be used to
support the CS's. The functionality of the current tool only
extracts data for stars in the fields of exposures in a proposal,
but it does not perform the bright object analysis. The input data
describing the exposures is read from databases here at STScI.
The standalone CS tool will process the field stars through the
bright object checker engine and generate the same files as the PI
tool.
VTT Objects Which Support Bright Object Checking
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Aperture
The currently selected aperture in the VTT.
Catalog
A particular catalog which the VTT can overlay.
BrightObjectChecker
The core engine with an interface that supports the inputs:
* Celestial Area on the Sky
* Aperture/Detector
* List of Optical Elements
and the outputs:
* A list of astronomical objects
* For each astronomical object
+ Parameters such as id, ra, dec, etc.
+ For each severity level, the maximum exposure time
before the level is exceeded
BrightObjectAnalysis:
Contains data related to the bright object analysis of a particular
aperture:
* enabled:
A flag indicating if bright object checking is turned on or
off.
* analysisArea:
Celestial area over which bright object checking has been
done.
* spectralElement:
The spectral elements for which bright object checking has
been done.
* exposureTime:
Exposure time to which the bright object analysis has been
applied.
* catalogs:
A set of catalogs containing the objects in the
analysisArea. There is one catalog one for each severity
level. The catalog data includes information about each
object including the severity level.
Possible User Actions and Consequences in the VTT
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The possible user actions associated with bright object checking
in the VTT are:
- Add an aperture
- Set bright object checking parameters
- Turn on bright object checking
- Turn off bright object checking
- Move or select an aperture
When bright object checking is performed in response to a user action,
the following tasks are performed:
Add an Aperture
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Create an associated BrightObjectAnalysis object with default
parameters and disabled.
Set Bright Object Checking Parameters
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Bring up dialog enabling the user to:
* Turn bright object checking on or off.
* Change spectral element. (When exiting the dialog, this will
cause bright object checking to be run on the spectral
elements regardless of whether or not bright object checking
is enabled.)
* Set the exposure time for each spectral element. (This will
cause the BrightObjectAnalysis object to regenerate the
severity level catalogs since the thresholds for each
severity level depend on the exposure time.)
* Set the objects to display, ie, those with health and
safety, science and/or no concerns.
* Set the default celestial area to be analyzed. The parameter
is actually a percentage value applied to the aperture.
Turn On Bright Object Checking
------------------------------
Set the BrightObjectAnalysis enabled flag to on.
If bright object checking has not yet been performed on the current
observing mode, then
Set the area to be analyzed to the default celestial area, i.e,
the desired percentage bigger than the aperture.
else
Set the area to be analyzed to be the areas in the aperture not
already analyzed.
If the size of the celestial area to be analyzed is not zero, then
Run the BrightObjectChecker.
Regenerate the catalogs for each severity level based on the
exposure time and add to the VTT Overlay Catalogs.
Turn on the desired severity level catalogs in the VTT Overlay
Catalogs.
Add the area just analyzed to the total analysisArea.
Turn Off Bright Object Checking
-------------------------------
Set the BrightObjectAnalysis enabled flag to off.
Remove the severity level catalogs from the catalog list.
Move or Select an Aperture
--------------------------
If BrightObjectAnalysis is enabled, then
If the aperture is not wholly inside the analysis area
Set the area to be analyzed to be the areas in the aperture
not previously analyzed.
Run the BrightObjectChecker
Regenerate the catalogs for each severity level and add to
the VTT Overlay Catalogs.
Turn on the desired severity level catalogs in the VTT
Overlay Catalogs.
Add the area just analyzed to the total analysisArea.
