ACT Data analysis

TOD ANALYSIS

April 2022 measurements were taken such that, beyond CLASS, also ACT is illuminated by the drone. ACT sees the drone in its near field. The code has been slightly modified in order to fit ACT specs (e.g. no VPM, nor boresight rotation) and analysis purpouse, here more oriented in getting the beam maps . So, only the detectors that survive after the cuts are analyzed.

The Zeus server stores the results (image files) archived in: /storage/drone/field_tests/TOCO/20220429/Analysis/Results_ACT/

Currently, PA5 (90/150 GHz) TODs of the April 29th (2022) flights have been processed based on detector crossing distance (both in azimuth and elevation) and time separation between crossing. As the typical timestream signal is pretty noisy, peaks are detected after smoothing the raw timestream with a 3 Hz lowpass filter. Detectors and the corresponding indexes in the TODs samples grouping all the detectors sensitive to each of the crossings, such that is possible to get one-pass maps for each of them. For each crossing two plot are produced. The first one, whose files are named with the scheme Fxx_FLYxxx_fxxx_uid_xxx_ctime_xxx_rxxcxx, where F and FLY are the flight numbers identities, f is the frequency, uid is the detector index in the array, which correspond to a certain r (row ) and c (column) of the readout. It contains the following subplots:

Plot 1: Full TOD. The section corresponding to the current crossing is marked.
Plot 2: Extracted section of the Full TOD corresponding to 12 seconds) around the time of the current crossing, also reporting telescope azimuthal speed and azimuth.
Plot 3: FFT of the extracted section. The location of the 47 Hz chopper frequency is marked in the plot.
Plot 4: The extracted section is filtered with a 3 Hz lowpass filter to retrieve the base signal of the crossing and with a 46-47 Hz bandpass filter to extract any component corresponding to the chopped signal.

Figure 1 - Flight 1 (150GHz), alt-scan, no chopping. Notice no power in the FFT at the 47 Hz mark and no chopping signal (orange, last plot).

OFFSET ANALYSIS

The second plot (files named offset_FLYxxx_fxxx_uid_xxx_ctime_...) contains two subplots: the upper one is, again, a zoom of the extracted section, focused on highlighting the choice of the distance minimum corresponding to the peak signal. In fact, crossings often happens near turnarounds, causing several distance minima to happen in the same extracted chunk, and also introducing uncertainties on telescope scanning speed (which accelerates during turnaround). Further, the scan only cover 4 degrees in azimuth. This step is critical to have a good estimation of the delays-anticipations we want to measure. The bottom plot shows the raw data, and two different lowpass filters (sine and butter) to get the actual instant when a crossing is detected.

Histograms and array plots of offsets

Further, a text .dat files is also produced. Each line correspond to a crossing. For each of them is reported the uid, ctime_crossing, ctime_approach, and the coordinates of both telescope and azimuth at the crossing. This is used for the subsequent calculation and analysis of the offsets angles and distribution across the array. The analysis to convert the delays/anticipations into a vector displacement accounts for horizontal and vertical motion of the drone and horizontal motion of the telescope, assuming both telescope boresight and the drone move a flat plane throughout the TOD (4 square degrees). For each detector, a variable number of crossing is seen; for each of them, a delay (or anticipation) of the drone with respect to the telescope. This time interval is converted in an angular distance multiplying by the relative velocity; the arc tangent of the vertical/horizontal speeds provides the orientation

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