Pre-processing

Overview

In terms of data processing, the HFI ground segment handles two types of data, both made available via the MOC:

• telemetry data transmitted from the satellite. These come from the different subsystems of the satellite service module, from the sorption cooler and from the two instruments.
• auxiliary data. These are data produced by MOC. The only 3 products used by the HFI DPC are the pointing data, the orbit data, and the time correlation data.

All data are retrieved by the HFI DPC level 1 software and stored in the HFI DPC database.

Telemetry data

The digitized data from the satellite are assembled on board in packets according to the ESA Packet Telemetry Standard and Packet Telecommand Standard, the CCSDS Packet Telemetry recommendations and the ESA Packet Utilization Standard.The packets are dumped to the ground during the Daily Tranmission Control Period, consolidated by and stored at MOC. Telemetry data contain the housekeeping data and the bolometer (ie science) data.

Housekeeping data

For several reasons (systems monitoring, potential impact of the environment, understanding of the bolometer data), the HFI DPC gathers and stores in its database the satellite subsystems housekeeping parameters:

• Command and Data Management System
• Attitude Control & Measurement Subsystem
• Thermal Control System
• Sorption Cooler System
• HFI housekeeping parameters

The structure and the frequency of the packets built by these subsystems and the format of the house keeping parameters are described in the Mission Information Bases [refer to an hypothetical MIB section under MOC responsibility]. The HFI L1 software uses these MIBs to extract the house keeping parameters from the packets. Given the status of each subsystem, the parameters are gathered in the HFI database in groups. The HFI L1 software builds in each group a vector of time (usually named TIMESEC) and a single vector per housekeeping parameter.

Bolometer data

The HFI science data is retrieved and reconstructed as described in section 3.1 page 5 Planck early paper VI .

Transfer functions

In order to ease the reading data in the HFI database, so called transfer functions are created. They allow software items to read data on which functions are applied on the fly. A simple example of a transfer function is the conversion of a thermometer data in Analogic to Digital Units (ADU) to Kelvins. Here we show the transfer function applied on the bolometer samples:

[math]HFI\_Signal\_V_{bc} = \frac{\frac{HFI{\_C}_{bc}}{N_{sample} - Nblanck_{bc}}- offset_{bc}}{F1_{bc}} \times \frac{Gamp_{ETAL}}{Gamp_{bc}} [/math]

where: [math]bc[/math] refers to a bolometer usually labelled by its electronic belt and channel. Eg. bc=00 refers to the a part of the first 100 GHz Polarized Sentivite Bolometer. [math]HFI\_Signal\_V_{bc}[/math] is the bolometer signal in Volts [math]HFI{\_C}_{bc}[/math] is the bolometer sample in ADU [math]N_{sample}[/math] is the number of samples in half a modulation period [math]Nblanck_{bc}[/math] is the number of samples suppressed at the beginning oft each half modulation period [math]offset_{bc}[/math] is close to 32768 [math]Gamp_{ETAL}[/math] is the gain amplifier mesured during the calibration phase. For bc=00, [math]Gamp_{ETAL}[/math] is equal to 1. [math]Gamp_{bc}[/math]

Statistics on the telemetry data

-	Nominal mission	Scientific full mission	From launch to the end of full mission
Duration		884 days	974 days
Number of HFI packets generated onboard (HSK/science)
Number of HFI packets generated onboard (HSK/science)
Number of HFI packets lost on board (HSK/science)
Number of HFI packets lost on ground (HSK/science)
Number of retreived HFI packets (HSK/science)
Number of missing raw data packets/samples (HSK/science)
Number of data raw data samples stored in the database (HSK/science)
Number of different housekeeping parameters stored in the database (HFI/SCS/sat)
Number of pointing samples stored in the database

Pointing data

The pointing data are built by the MOC Flight Dynamics team. The pointing data are made available to the DPC via AHF files. See AHF description document and [refer to the PLA AHF folders] AHF files repository. All data in the AHF files are ingested in the HFI database. They’re then interpolated to the bolometer frequency [refer to the Karim’s section].

Orbit data

Satellite orbit velocity is built by the MOC Flight Dynamics team and made available to the HFI DPC via orbit files. See Orbit description document and [refer to the PLA orbit files folders] orbit files repository. As those orbit files contain both effective and predictive data, they are regularly ingested updated in the HFI database.
Note: these same data are also ingested in parallel into the NASA JPL Horizons system (http://ssd.jpl.nasa.gov/) under ESA’s responsibility.

The satellite orbit data preprocessing is the following.

• The sampling of the MOC provided orbit velocity data is appromximately 1 every 5 mn. These data are interpolated to the time of the middle of the HFI rings.
• The reference frame of the orbit data is translated from the MOC given Earth Mean Equator and Equinox J2000 (EME200) reference frame to the ecliptic reference frame in cartesian coordinates.
• The earth velocity provided by the NASA JPL Horizons system (http://ssd.jpl.nasa.gov/) is interpolated to the time of the middle of the HFI rings. It is then added to the satellite velocity data.

The use of the satellite orbit velocity is two-fold: it is used to compute the CMB orbital dipole (see calibration section) and to compute the positions of solar system objects (see data masking section).

Time correlation data

The MOC is responsible for providing information about the relationship between the satellite On Board Time (OBT) and Universal Coded Time (UTC) [refer to a hypothetical Time Management section]. This information comes via several measurements of OBT and UTC pairs each day, measured during the satellite ranging. See Time Correlation document and [refer to the PLA TCO folders] Time Correlation files repository.

OBT-UTC correlation data

The plot shows the (OBT, UTC) data couples provided by MOC since Planck launch. The x axis is in number of days since the 17th of May 2009 while the y axis is the difference of OBT and UTC in seconds. The very slow drift is approximately 0.05 seconds per day. The small wiggles are due to the satellite global temperature trends due to its orbit and distance to the sun. Note: The extra couple on the 1st of June 2010 is not significant and due to a misconfiguration of the ground station parameters.

An order 3 polynomial is then fitted to the data. As the whole HFI data management and processing uses OBT, the OBT-UTC information is only used when importing orbit data from Horizons.