Statistical Properties of Geosynchronous Satellite Photometry

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1 Statistical Properties of Geosynchronous Satellite Photometry Tamara E. Payne Applied Optimization Inc. Abstract This paper presents the general properties of a set of observations of satellites in Geosynchronous Earth Orbit (GEO) made between 2004 and A statistical analysis of the photometric properties of the forty-seven satellites sampled is discussed. The sample contains satellites with ten different bus types or configurations. The satellite brightness distributions are shown for five different visible bandpasses. The brightness distributions are analyzed as a function of season and phase angle. Introduction Forty-seven different satellites were observed between the years 2004 and These observations are the basis for the statistics presented today. The satellite sample consists of ten different types based on the satellite configuration; satellite body and solar panels. The photometry was collected in five different bandpasses, in different seasons, and at different phase angles. Using the standard astronomical methods, the photometry is reported in exo-atmospheric magnitudes in broadband astronomy filters. The brightness distributions of this sample were analyzed on the basis of four variables; bandpass, season, phase angle, and satellite type. Results The results of the statistical analyses will be shown for 1. Visible bandpasses 2. Season 3. Phase angle 4. Satellite type The frequency distributions of the observations for each bandpass are shown in Figure 1. The histogram consists of the number of satellite observations in each magnitude bin, shown on the y-axis of each graph. The brightnesses (x-axis) are shown in magnitudes, in bins of two magnitudes each. In Figure 1 are the brightness distributions of the sample in each of the five bandpasses in the visible region of the electromagnetic spectrum. As you can see, the majority of satellites have brightnesses in the range of ten to twelve magnitudes. This is fairly consistent for the different bandpasses.

2 Figure 1 Frequency distributions of GEO observations in different visible bandpasses The histograms showing the frequency distributions of observations of GEOs during different seasons are shown in Figure 2. This sample is brighter during the Vernal Equinox and Winter, and respectively; whereas the sample is fainter during the Summer and Autumnal Equinox, and respectively.

3 Figure 2 - Frequency distributions of GEO observations during the four different seasons The phase angle is defined for the purposes of this work as the angle between the sun and the satellite as seen from the sensor. For the analysis of the brightness distributions as a function of solar phase angle, the phase angles were divided into three groups: low, medium, and high. Low is for angles less than 10 degrees; medium is for angles between 20 and 40 degrees; and high is for angles greater than 40 degrees. The median magnitude for each set of brightnesses is shown in each panel of Figure 3. The satellites are brighter in the low phase angle group and fainter in the high phase angle group by almost one magnitude.

4 Figure 3 - Frequency distributions of GEO observations under different phase angle conditions Finally, the brightness distributions of the observations will be compared for different satellite types. The sample contains observations of GEOs with ten different satellite types. They are A2100 A2100A A2100AX AS 4000 and AS 7000 BSS601 BSS702 Eurostar 3000 FS1300 Spacebus 2000 and 3000 Star 2

5 The next set of figures (Figures 4 6) contains the histograms for these satellite types. Figure 4 shows the first three types. The distributions show that most brightnesses are in the 12 th magnitude range. A2100 has a large number of measurements at 14 th magnitude as well. Figure 4 - Frequency distributions of GEO observations for bus types: A2100, A2100A, and A2100AX The next three types in Figure 5 show that these types similarly have brightnesses of around 12 th magnitude. AS4000 and AS7000 also have many fainter observations at 14 th magnitude and BSS702 has many brighter observations at 10 th magnitude.

6 Figure 5 - Frequency distributions of GEO observations for bus types: AS4000/7000, BSS601, and BSS702 Figure 6 shows the distributions for the final four satellite types. Again, most measurements show the brightnesses to be around 12 th magnitude. However, Eurostar 3000S type has many brighter measurements at 10 th magnitude. The Star 2 bus type has many fainter measurements at 14 th magnitude. Overall, BSS702 and Eurostar3000 satellites tend to have brighter observations than the other types in the sample whereas Star 2 satellites tend to be dimmer.

7 Figure 6 - Frequency distributions of GEO observations for bus types: Eurostar3000, FS1300, Spacebus2000/3000, and Star2 Conclusions Using this sample of photometric measurements of three-axis stabilized GEO satellites, the average brightnesses were shown to range between 10 and 12 magnitudes with the brighter and fainter exceptions noted. How the brightness distributions vary with four variables was studied. These four variables were bandpass, season, phase angle, and satellite type.