*** CRUSH User's Manual Extension for LABOCA *** Attila Kovacs Last updated: 20 February 2016 Table of Contents ================= 1. Introduction 3. Glossary of PolKa-specific options 4. PolKa-specific log quantities ##################################################################### 1. Introduction ##################################################################### PolKa is the polarimetry frontent for the APEX/LABOCA camera. This document contains information specific to using CRUSH-2 to reduce PoLKa data. It is assumed that you are already familiar with the contents of the main CRUSH-2 README (inside the distribution directory), especially its Section 1 (Getting Started), as well as the APEX and LABOCA specific user's guide extensions (apex/REAME and laboca/README). If you run into difficulty understanding the concepts in this document, you will probably find it useful to study the prerequisite README documents a little longer. ##################################################################### 2. Glossary of PolKa-specific options ##################################################################### :: analyzer= @Since: 2.04 Specify that the analyzer grid position that was used for taking the data. Specifying the analyzer is important for recovering the polarization information. The must be either 'H' or 'V' corresponding to the two positions. As of 2011, the analyzer position should be correctly recorded in the data file, and therefore automatically detected. You can still use 'analyzer' to override the recorded setting. :: analyzer.h=X @Expert @Since: 2.11 Set the H analyzer angle (in degrees). @See: 'analyzer.v' :: analyzer.h.phase=X @Expert @Since: 2.11 Set the relative phase (degrees) of the total-power modulation for waveplate phase reconstruction with the H analyzer. These phases can be measured using 'waveplate.tpchar' when the waveplate data is normally present. @See: 'waveplate.tpchannel', 'waveplate.tpharmonic' 'waveplate.tpchar', 'analyzer.v.phase' :: analyzer.v=X @Expert @Since: 2.11 Set the V analyzer angle (in degrees). @See: 'analyzer.h' :: analyzer.v.phase=X @Expert @Since: 2.11 Set the relative phase (degrees) of the total-power modulation for waveplate phase reconstruction with the V analyzer. These phases can be measured using 'waveplate.tpchar' when the waveplate data is normally present. @See: 'waveplate.tpchannel', 'waveplate.tpharmonic' 'waveplate.tpchar', 'analyzer.h.phase' :: filter.hwp @Advanced @Since: 2.11 Use FFT filtering to get rid of the total-power modulation by the half-waveplate rotation. Can be used together with, or instead of, 'purify'. The advantage of the FFT filtering is that it works even if the waveplate data is not entirely accurate (i.e. jittery). However, if the waveplate phase is fully known, then 'purify' should be the prefered method for rejecting the unwanted total-power modulation. The number of harmonics (over the rotation frequency) is controlled by the 'harmonics' subkey. @See: 'filter.hwp.harmonics', 'waveplate.jitter' 'purify', 'waveplate.frequency' :: filter.hwp.harmonics=N @Expert @Since: 2.11 Specify how many harmonics of the waveplate rotation frequency to use in the half-waveplate filter. @See: 'filter.hwp' :: purify @Advanced @Since: 2.11 Really a generic option for getting rid of unwanted signals before the mapping step. The exact action may be different from one instrument to another. For now, only PolKa uses this option for removing the total- power modulation before producing the Q and U maps. The method uses a template of the modulation as a function of the phase. It should work perfectly, if the waveplate angles are accurately known. However, FFT filtering (via 'filter.hwp') is more suited for uncertainties in the waveplate angles. @See: 'filter.hwp' :: source.polar @Advanced Specify to yield polarization data (I,Q and U) rather than simply producing a total-power image. The option obviously only affects instruments that measure polarization, anbd will be ignored otherwise. You can also use the shorthand 'pol' to the same effect. @See: 'pol', 'spf', 'waveplate.refangle', 'analyzer' :: source.polar.angles @Since: 2.11 @Advanced Write an image of the polarization angles also. The shorthand 'spa' can also be used. @See: 'spa' :: source.polar.fraction @Since: 2.10 @Advanced Write an image of the polarized power fraction as well as the default polarization products (N, Q, U and the derivatives I & P). You can also use the shorthand 'spf' to the same effect, and can control the clipping of the noisy bits via the 'rmsclip' sub-option. @See: 'spf', 'source.polar', 'source.polar.fration.rmsclip' :: source.polar.fraction.rmsclip=X @Since: 2.10 @Expert Set the maximum rms for the unflagged points in the polarization fraction image. The default value is 0.03 (i.e. 3% rms). You can also use the shorthand version 'spf.rmsclip'. @See: 'spf', 'source.polar.fraction' :: waveplate.channel=N @Expert Specify the LABOCA channel (counting from 1) that carries the waveplate phase information. The waveplate phases are critical to recovering the polarization information from the data. @See: 'waveplate.fchannel', 'waveplate.refangle' :: waveplate.counter @Advanced @Since: 2.11 Occasionally the waveplate spins backwards. This option lets you reduce such data, provided you know when this happened. :: waveplate.despike=X @Expert @Since: 2.11 When fitting the timestamp data, assuming regular waveplate rotation (see 'waveplate.regulate'), this option can set a despiking level. @See: 'waveplate.regulate' :: waveplate.fchannel=N @Expert The LABOCA channel number (counting from 1), which contains the frequency information for the last waveplate cycle. This information is not used by crush really, but may point the user to where to find this information in the raw data, if one wishes to look into the details. @See: 'waveplate.channel' :: waveplate.frequency=X @Obsolete @Expert Specify the waveplate frequency (in Hz) to assume when detailed waveplate information is not readily available. The waveplate angle of the first frame can be set via 'waveplate.refangle'. @See: 'waveplate.channel', 'waveplate.refangle' :: waveplate.incidence=X @Expert @Since: 2.11 The waveplate incidence angle from normal, in degrees. @See: 'waveplate.incidence.phase' :: waveplate.incidence.phase=X @Expert @Since: 2.11 The waveplate phase (in degrees) of the plane of incidence, measured from the reference position in the direction of waveplate rotation. @See: 'waveplate.incidence' :: waveplate.jitter=X @Expert @Obsolete Specify the typical fractional waveplate jitter. This information is used for designing optimal notch filters for the total-power mode to reject any waveplate modulated residues. This option has been obsoleted by the new time-domain filter, and will dissappear in future releases. @See: 'waveplate.channel' :: waveplate.oversample=X @Expert @Since: 2.04 Define the oversampling rate for the total-power modulation removal. Typically, a waveplate rotation (1.560 Hz) is 16 samples (at 25Hz sampling rate), only coarsly resolving the power modulation waveform. Because the waveplate rotation is not completely synchronous with the acquition, it may help to model the waveform at somewhat higher resolution for a better removal of the unwanted total-power modulation signals. The default value is 1.0. @See: 'waveplate.channel' :: waveplate.refangle=X @Advanced Set the waveplate angle at its reference position. The calibration of this position is necessary for obtaining meaningful polatization angles. Without it only the polarized fluxes, or polarization fractions can be measured. The calibration of the reference angle requires measurements on sources of known polarization (e.g. a wire grid in the pupil) @See: 'waveplate.channel' :: waveplate.regulate @Advanced @Since: 2.11 Provide a workaround to the innacuracy of the waveplate timestaps, by assuming that the waveplate motion is regular. A linear fit to the timestamp data will be used instead of the original timestamps. The quality of the fit may be improved with despiking the data via 'waveplate.despike'. Requires timestamp information via 'waveplate.tchannel'. @See: 'waveplate.despike', 'waveplate.tchannel' :: waveplate.tchannel=N @Expert @Since: 2.11 The channel that holds the timing offsets to the last waveplate timestamp. This information can be used by CRUSH to fully reconstruct the waveplate motion (at least to the timestamping accuracy). :: waveplate.tpchannel=N @Expert @Since: 2.11 Reconstruct the waveplate data, when this is not recorded (such as for two days in Dec 2011), from the total power-modulation of the specified channel. The harmonic and relative phase of the total power modulation (for H and V analyzers respectively) are set by 'waveplate.tpharmonic', 'analyzer.h.phase' and 'analyzer.v.phase' @See: 'waceplate.tpharmonic', 'analyzer.h.phase' 'analyzer.v.phase' :: waveplate.tpharmonic=N @Expert @Since: 2.11 The harmonic of the waveplate frequency that should be used for the waveplate phase reconstruction, when the waveplate phase data is not recorded. @See: 'waveplate.tpchannel' ##################################################################### 3. PolKa-specific log quantities ##################################################################### analyzer The analyzer in place ('H', 'V' or '-') wpdelay The mean time-stamping delay (ms) of the waveplate reference crossings based on the linear fit from 'waveplate.regulate' wpdir Direction of waveplate rotation ('+' or '-') wpfreq Waveplate frequency (Hz). wpjitter Fractional jitter of the waveplate. wpok Whether or not the scan has valid waveplate data. ------------------------------------------------------------------------------ Copyright (C)2016 -- Attila Kovacs