Instrument-Specific Software

Software for the High Speed Photometer is located in the hsp package, including the calibration task calhsp. The hsp package includes tasks that can be used to calibrate the High Speed Photometer, monitor the instrument's health, and reduce its data. The tasks are grouped below, based on their relation to the Routine Science Data Processing (RSDP), which is automatically performed at STScI on all science data received from the spacecraft. RSDP-related tasks include algorithms to generate the calibration coefficients for high voltage and gain factors, detector efficiency, dark signal, dead time, etc., as well as the calibration algorithm (calhsp), which applies all these correction factors to the observational data. Tasks not related to RSDP include those used to monitor the instrument's health (warm-up time determination, detector linearity verification, etc.), calibrate the polarimeter, locate the apertures, and other general tasks (spacecraft velocity and position determination, polynomial fitting and evaluation, etc.).

HSP Calibration Parameters Required by RSDP

Aperture sizes (CCP0) and dark aperture translations (CCP9) are not quantities that are calibrated with observational data. The rest of the above quantities, except paired-pulse correction (CCP8), have the identical formula in RSDP processing. They are expressed as a third-order, bi-dimensional polynomial function of temperature and time:

Where:

X is a calibration quantity,

X0 is the base value of X,

t is the observation epoch,

t0 is the reference epoch,

T is the temperature, and

T0 is the reference temperature.

Thus, sixteen coefficients are needed for each set-up combination (for example, in the case of analog gain factor, each detector ID and gain setting combination has 16 polynomial coefficients) in each relation. Paired-pulse correction is calibrated only as a linear function of temperature for each set-up combination (detector ID, voltage, and threshold setting).

Additional Calibration Parameters (Non-RSDP) for HSP

Non-RSDP tasks in this package can be put into four groups. The first group performs polarimetry calibrations, the second locates the aperture center, the third monitors instrument health, and the fourth performs miscellaneous functions.

- Polarimetry Calibrations:
- poleffv: Determines the polarization transmission coefficients of each of the Polaroid analyzers in the polarization detector, i.e., the amount of observed polarization of an ideal, 100% linearly-polarized target. This task uses data obtained by observing a target with different telescope roll angles. By comparing the result polarization with the target's known polarization value, the polarization transmission coefficients are acquired.
- polpav: Determines the polarization position angle offset from the standard equatorial coordinate system. This task's input data are obtained by observing a target with all four Polaroid analyzers. By comparing the resulting position angle with the target's known position angle, the position angle offsets can be calculated.
- polverify: Verifies the entire polarization data calibration procedure. A target is observed with one Polaroid analyzer at different roll angles and then the two previously-described corrections are performed. The result should agree with the known values.

- poleffv: Determines the polarization transmission coefficients of each of the Polaroid analyzers in the polarization detector, i.e., the amount of observed polarization of an ideal, 100% linearly-polarized target. This task uses data obtained by observing a target with different telescope roll angles. By comparing the result polarization with the target's known polarization value, the polarization transmission coefficients are acquired.
- Aperture Location Calibration:
- apercen: The first step ("Phase I") of aperture location calibration is to determine the aperture's center in the coordinate system used for the image dissector tube (IDT) deflections. This is done by observing an extended target that fills the aperture and scanning the aperture. The center coordinate is then obtained by fitting a circle to the edge of this two-dimensional image.
- imgscale: The second step ("Phase II") of aperture location calibration, is to establish the transformation coefficients between the IDT deflection coordinate system and the V2,V3 coordinate system. This is done by moving the pointing of the V1 axis to a matrix of sky positions to locate a point source target. The deflection coordinate of the target is obtained by doing an area scan at each pointing.
- lgaperloc and smaperloc: ("Phase III") The third stage of aperture location is to obtain the aperture's center coordinate to an accuracy of 0.02 arcseconds in the V2,V3 coordinate system. For small apertures (task smaperloc), this is done by moving the telescope pointing to a matrix of sky positions to locate a point source target. A circle is then fitted to the edge beyond which no flux can be obtained from the target. For large apertures the scheme is slightly different: an open cross pattern is used in place of a square matrix for pointings, and the center coordinate is similarly calculated from the edge coordinates.

- apercen: The first step ("Phase I") of aperture location calibration is to determine the aperture's center in the coordinate system used for the image dissector tube (IDT) deflections. This is done by observing an extended target that fills the aperture and scanning the aperture. The center coordinate is then obtained by fitting a circle to the edge of this two-dimensional image.
- Instrument Health Monitoring:
- abssenv: Compares the digital count rates and known fluxes of standard targets. Such comparison verifies the linearity of the detectors and the correctness of the entire calibration procedure. It also ties the instrument count rates to the absolute unit of flux or magnitude.
- aloglin: Verifies the linearity of analog data by comparing the analog measurements and known fluxes of standard targets. This task works like abssenv.
- flex: Determines the HSP optical bench flexure caused by temperature differences within HSP. This is also known as the "banana mode correction." A one-dimensional polynomial is used to fit the deflection coordinate deviation as a function of temperature differences.
- focusv: Determines the best HSP electronic focus setting by observing the same target with different focus settings. The setting having the highest count rate presumably has the least beam spreading, and therefore, is the optimum setting.
- phav: Determines the optimum threshold setting for the pulse amplifier and discriminator (PAD). A two-component (Gaussian and exponential) model is assumed to represent the noise generated from the detectors, and a least-squares fitting is used to obtain the model coefficients.
- scatterv: Determines the amount of scattered light from a bright source near, but outside, an aperture's view. This task produces a table of count rates from scattered light as a function of angular distances from the aperture center.
- taflat: Calibrates the flat field of HSP target acquisition apertures. A presumably uniform extended target is used for this calibration.
- warmup: Determines the time a detector takes to stabilize after its high voltage power supply is turned on. This quantity can be used in planning the instrument's schedule.

- abssenv: Compares the digital count rates and known fluxes of standard targets. Such comparison verifies the linearity of the detectors and the correctness of the entire calibration procedure. It also ties the instrument count rates to the absolute unit of flux or magnitude.
- General Tools:
- monitor: This task reduces the data obtained when HSP is operated as a space particle monitor. The result will primarily be used to delineate the South Atlantic Anomaly (SAA).
- parthitv: Removes particle events (data of abnormally high counts compared to their neighboring pixels) and calculates the mean count rate of a data file.
- polyeval: Evaluates polynomials representing the quantities needed by RSDP. This is a general tool used in many scripts to do partial calibrations.
- polyfit: Performs one-dimensional polynomial fitting. The task can fit any order of polynomial (up to nine), using a set of orthogonal polynomials.
- posvel: Calculates the position and velocity of the spacecraft, based on a fitted model from the flight ephemeris.
- twodpolyfit: Performs two-dimensional polynomial fitting. This will generate the final coefficients of the RSDP relations described above. This is a general tool that can fit any order of polynomials (up to 9 x 9), and it uses the singular value decomposition (SVD) algorithm.

- monitor: This task reduces the data obtained when HSP is operated as a space particle monitor. The result will primarily be used to delineate the South Atlantic Anomaly (SAA).

- RSDP-Related Calibration Software
- Non-RSDP-Related Calibration Software

Generated with WebMaker