Timelines

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General description[edit]


The timelines, or TOIs for Time-Ordered Information, are vectors of signal or of pointing or of some other quantity giving the value of that quantity as a function of time during the mission. The TOIs described here are sampled regularly at the the (instrument dependent) detector sampling frequency and span the full science mission. They thus consists of a large amount of data. This section is concerned with the signal TOIs and they associated pointing TOIs. For each bolometer the DPCs provide a single timeline of calibrated signal, ready for projection onto a map, and 3 timelines of coordinates, corresponding to the two angular coordinates and one position angle.

Obviously these vectors are very long (~1.38E10 samples for HFI, nnnn for LFI) and thus need to be split into multiple files for export. Here the data are split by Operational Day (OD) as follows:

  • HFI: 2 files per OD, one for pointing and one for signal, covering ODs 91 -- 974, all sampled at [math]F_samp \approx 180.3737 Hz[/math].
  • LFI: 6 files per OD, 3 each for signal and pointing, since the sampling frequency is channel dependent., and covering ODs 91--NNN.

The signal timelines are encoded as Real*4, but the pointing vectors had to be encoded as Real*8 to maintain the required accuracy. The result is that the total volume of the full dataset is ~30 TB.

TBW:

  • ROIs of offsets for HFI
  • baselines for LFI


Production process[edit]

HFI processing[edit]

The input TOIs are in ADUs representing the voltage signal at the end of the electronics (see Detection chain for details). The processing applied to remove instrumental effects and to calibrate them is described in detail in the HFI TOI processing section, and we give a very brief summary here for convenience. That pipeline performs the following operations:

ADC correction
corrects for the uneven size of the ADC bins.
demodulation
this is performed around a variable level which is determined from the valid input data (using a validity flag from a previous version of the processing), and the data are converted to engineering units (V) using known conversion coefficients.
despiking
the redundancy within a ring is used to determine where glitches occur. Once identified, the glitches are fitted with templates. A glitch flag is produced that identifies the strongest part of the glitches, and a timeline of glitch tails. produced from the template fits, is subtracted from the demodulated timeline. Finally, the flagged regions are replaced with data from an average over the pointing period in order to not leave holes in the timeline that would perturb the usage of Fourier methods on them
dark template removal
the two dark bolometers are demodulated and despiked as above; the resulting timelines are then smoothed and used as an indicator of the overall temperature variations of the bolometer plate. Where the variations are consistent with each other, they are combined and removed from the bolometer signal timelines using appropriate coupling coefficients. The few percent of the data where they are not consistent are flagged as not valid on the timelines.
conversion to absorbed power
the timeline is converted to watts of absorbed power using the bolometer function. This includes a non-linearity correction; removal of the 4K cooler lines: the electromagnetic interference of the 4K cooler with the bolometer readout wires induces some sharp lines in the signal power spectra at frequencies of the 4K cooler's fundamental and its multiples, folded by the signal modulations. Fourier coefficients of the relevant lines are determined on a per-ring basis, and then removed from the data. The quality of the removal depends on the bolometer.
deconvolution by the time transfer function
this is done to correct for the non-instantaneous time response of the bolometers. The function itself is modeled using up to 8 parameters which are adjusted primarily on the planet data and also from comparisons of the northward and southward scans of the Galactic Plane. It is then removed using Fourier techniques, which has the side-effect of increasing the noise at high frequencies.
jump correction
removes some (relatively rare: 0.3 jumps per bolometer per pointing period, on average) jumps in the signal baseline. The jumps are detected characterized on smoothed TOIs, and corrected by adding a constant to part of the signal timeline. The origin of the jumps is not known.

The results of this processing are a timeline of signal (in absorbed watts) and a valid data flag timeline for each of the 50 valid bolometers processed; these timelines contain the full sky signal, i.e., including the solar and orbital dipoles, the Zodiacal light, and contributions from the Far-Side lobes. The dipoles are necessary for the flux calibration and are removed at the mapmaking stage. The remaining two bolometers (143-8 and 545-3) show semi-random jumps in the signal level, typically jumping over 2-5 different pseudo-baseline levels, a behavior known as Random Telegraphic Signal, so that these are commonly called the RTS bolometers. Finally, ring-level statistics of different types (mean, median, rms, kurtosis, etc.) are determined on a per-ring basis for all timelines, and a selection based on these statistics is used to discard anomalous rings, which are recorded in a ring-level flag for each valid bolometer timeline (see the Discarded rings section).

Throughout this processing, Jupiter is masked in the timeline in order to avoid ringing effects in the processing (thanks to various improvements in the despiking and in the transfer functions it is no longer necessary to flag weaker planets as was done in Release 1). Since they move on the sky, the portion of the sky masked during one survey is observed during one, and no hole is left in the final map. In parallel, the planet data are processed in a similar way, but with different parameters for the despiking step, and without the final jump correction step. These results are processed separately to determine the beam shapes and the focal plane geometry.

Finally, the TOIs are calibrated in astrophysical units using the results of the calibration the calibration pipeline, described in the Map-making and calibration section, which are stored in the IMO, and the best estimate of the zero-point offsets (a constant level for each bolometer) and of the far-side lobes (another signal TOI determined from the input TOI) are removed. These TOIs are ready for projection onto a map. That projection normally requires that the low-frequency noise be removed via a "destriping" (sometimes called "baseline removal") step. The HFI-DPC does its destriping at ring-level; should the user want to use the DPC's offsets, they are provided separately ([##REF##]).

The pointing (see common Detector Pointing section for details) is determined from the AHF produced by MOC, which gives the direction and orientation of the LOS of a fiducial position in the focal plane at frequencies of 8Hz during stable pointing and 4 Hz during maneuvers. This is interpolated to the times of data observations, corrected for the wobble and other time-dependent offsets determined from the observed positions of a large number of sources around the sky, and finally converted to the LOS of each detector using the quaternions in the IMO.


File Names[edit]

are of the form

HFI_TOI_353-SCI_v100_ODnnnn.fits


FITS file structure[edit]

(Planck) High Frequency Instrument

(Planck) Low Frequency Instrument

Operation Day definition is geometric visibility driven as it runs from the start of a DTCP (satellite Acquisition Of Signal) to the start of the next DTCP. Given the different ground stations and spacecraft will takes which station for how long, the OD duration varies but it is basically once a day.

analog to digital converter

sudden change of the baseline level inside a ring

random telegraphic signal

Data Processing Center

Attitude History File

[ESA's] Mission Operation Center [Darmstadt, Germany]

Line Of Sight

Flexible Image Transfer Specification