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Data: The First Intensity Map


The first priority was to ensure that the telescope was accurately pointed. To ensure this, the fastenings on the telescope were checked and a pointing test was conducted via the offset method. Next, the command file for movement and data acquisition was written. The coordinates to be integrated were Galactic as this provided subsequent simpler data reduction and analysis. The time commands in the file were chosen specifically to maximise the amount of data points that could be taken in any one session. It must be noted however that many of the coordinates were out of limits for the telescope simply because of the time of day (e.g. below the horizon or beyond the limits of the telescope). This meant that the integrations for these coordinates had to be repeated at a different time frame and so multiple 'passes' were needed to ensure full coverage.

The coordinates chosen were: l=0-180, b=+/-10. Where: l is the Galactic longitude and b is the Galactic latitude. These coordinates incremented in steps of 2 for longitude and 5 for latitude. The beamwidth of the telescope is 5, and so by sampling every 2 in longitude the data is 'over sampled' providing additional integration in the final analysis. To choose the bandwidth, consideration had to be given to the balance between sensitivity and resolution. It was felt that a small bandwidth would increase the sensitivity of the integration as it would filter noise either side of the frequency width chosen. This inherently reduces the frequency resolution of the telescope, but it was felt that the resolution was of secondary importance to the sensitivity. For this reason a bandwidth of 40KHz was chosen.

Another advantage of choosing a small bandwidth is the reduction in integration time. Scanning through a larger frequency domain would increase the time for one integration and hence increase the overall time for all the data to be taken. This is of paramount importance considering the short time frame in which to take the data. This is due to the fact that the timescale for data reduction is very small and consequently the telescope needed to take the data relatively quickly. The integration time per Galactic coordinate was 60s as this was felt to include an adequate number of frequency scans.

The data that was recorded, however, is not calibrated. To achieve this, a recording of the sun was taken at regular intervals throughout the session and compared to known values. This was used to scale the intensity of the results for the Galactic coordinates to provide consistent data.

Acquisition of Data

As indicated in the user manual, the data is recorded in a text file with the extension '.rad'. The file contains all pertinent data for analysis, including: Frequency, Intensity, Commands given by user, Time of recording. Unfortunately, the data is not in a usable format for analysis. It must be manipulated in the file and transferred to a package such as Excel in order to make sense.