Abstract
In the preceding chapters, we have discussed the satellite orbit, position, and ground track. All this can be deduced from the position S of the satellite as viewed from the center of attraction O, which is the center of the Earth. The time has come to look at things from a different standpoint: we shall now be concerned with the view from an instrument carried aboard the satellite. The main difference is that we are now looking at things from the point of view of the satellite S. As a consequence, this chapter is principally concerned with observation satellites.
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Notes
- 1.
The axes are sometimes taken in a different order, with a different orientation, e.g., \(\boldsymbol{SZ}_{\mathrm{c}}\) pointing in the opposite direction to the nadir. However, in every case, the triad is right-handed and orthogonal and the direction of the nadir corresponds to one of the axes.
- 2.
The word “pixel” was coined in 1969, by contracting picture and element.
- 3.
To get some idea, on those satellites which carry it, the instrument known as ScaRaB investigates the radiation budget by scanning every 6 s. The effective part of the scan lasts for 3.18 s. For the remaining 2.82 s, the instrument does a calibration sighting and repositions itself.
- 4.
Charge-coupled devices (CCD) can acquire a row of pixels (1D-CCD, one dimension) or several rows (2D-CCD, two dimensions). Aboard SPOT-4, the HRVIR instrument uses the so-called push-broom mode with a 1D-CCD. The optical instrument is based on a telescope whose field of view is covered instantaneously by a row of 1,728 detectors, each corresponding to one pixel. In the case of the POLDER instrument, carried aboard ADEOS-1 and -2 and Parasol, the use of 2D-CCDs makes it possible to acquire a set of rows simultaneously, rather than just one.
- 5.
The nadir is the direction given by the vertical, looking downwards, i.e., toward the center of the Earth. The opposite direction is the zenith. The word “nadir” comes from the Arabic nāḍir, from the root of the verb “to look straight at.”
- 6.
In Arabic, semt er-rās means “the path of the head.” This gives the word “zenith,” the point on the sky just above the head. The word “azimuth” comes from as-semt, “the path,” with assimilation of the article.
- 7.
There are in fact six versions of this instrument: PFM (Proto Flight Model) aboard TRMM, FM1 and FM2 aboard Terra, FM3 and FM4 aboard Aqua, and FM5 aboard NPP. These instruments FM can operate in cross-track or variable-yaw mode as required.
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Capderou, M. (2014). View from the Satellite. In: Handbook of Satellite Orbits. Springer, Cham. https://doi.org/10.1007/978-3-319-03416-4_12
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DOI: https://doi.org/10.1007/978-3-319-03416-4_12
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