Pointing

Pointing analysis of the CLASS data

Analysis 20230222-FLY022 S90

Delay times for valid crossings away from turn arounds

Pointing Errors

We modeled the beam as a 2D Gaussian and computed the impact parameter of each crossing event based on the amplitude of the signal. Then we used the direction of the relative motion of the drone to estimate the location of the impact (nearest approximation of the drone to the center of the beam). Finally the pointing errors could be determined by comparing to the location of the drone (based on the GPS) at the same instant of the peak signal.

Maps

Map 150 GHz

Map 220 GHz

After deconvolving time constants and synchronizing with the VPM

Telescope Recentering

Given the difficulty to determine the exact coordinates of the central ray of the telescope, the source is detected with an offset from the central pointing of the telescope. We use the offsets obtained from the crossing analysis to fit the position of the telescope, thus recentering the source image. We expect that the offset needed will be shared by all the flights from the same day, as they all share the same GPS coordinate system determined by the coordinates of the GPS base station.

For FLY022, on 20230222, the correction applied on the telescope position was [E, N, U] = [-0.210, 0.483, 0.492] meters.

Centroids per scan passes. Still cannot identify the source of the 0.01 deg offset.

Recentering of all 20230222 flights (g_band in mount 2)

We fit the telescope position out of all the flights avaliable in 20230222 for the g_band (mount2). The results were the following:

# dE [m], dN [m], dU [m]

FLY021 -0.181441, 2.275975, -1.530999

FLY022 -0.209762, 0.425587, 0.424830

FLY023 -0.420987, 0.313521, 0.308325

FLY024 -0.383654, 0.422487, 0.428952

FLY025 -0.443130, 0.301869, 0.306619

FLY027 -0.484419, 0.230367, 0.226285

FLY028 -0.537827, 0.217457, 0.228238

FLY029 -0.584082, 0.097574, 0.092785

FLY030 -0.376284, 0.373615, 0.370786

FLY036 -0.298372, 0.428042, 0.417377

We discard FLY 021 because it is too different from the rest. Then compute the mean of each coorrection, which is understood as a correction to the location of the main ray entering the telescope, for g_band in mount2.

(dE [m], dN [m], dU [m]) = (-0.415, 0.312, 0.312)

It is very interesting that dN = dU. This could be due to a systematic error, but we still haven't understood the reason for such an agreement.

Time mismatch in FLY025 (1 second!)

We found that FLY025 has a 1 second mismatch (delay) between the GPS and TOD data. This can be seen in the dAlt offsets

After adding 1 second to the drone GPS time data, the problem goes away. We still don't know why this happened. The problem did not affect the other flights.

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