Observing Polar Regions from Space: Comparison between Highly Elliptical Orbit and Medium Earth Orbit Constellations

Abstract

Continuous observation of polar regions from space remains an important unsolved technical challenge of great interest for the international meteorological community. This capacity would allow achieving global continuous coverage once combined with the geostationary (GEO) satellite network. From a practical point of view, continuous coverage of polar regions with a small number of spacecraft can be obtained from a constellation of satellites either in highly elliptical orbits (HEO) or in medium Earth orbits (MEO). The study compares HEO and MEO satellite constellations for their capacity to provide continuous imaging of polar regions as function of the viewing zenith angle (VZA) and evaluates the corresponding latitude limits that ensure sufficient overlap with GEO imagery. Earlier studies assumed the latitude boundary of 60° and the VZA range 70°–85° depending on the space mission focus: meteorological purposes or communications. From the detailed analysis of meteorological retrieval requirements, this study suggests that the overlap of the GEO and polar observing systems (HEO or MEO) should occur down to the latitude band 45°–50° with a maximum VZA ranging between 60° and 64°. This coverage requirement can be met with two sets of three-satellite HEO constellations (one for each polar area) or a six-satellite MEO constellation. The 12-h Molniya and 14-, 15-, and 16-h HEO systems have been analyzed and determined to meet these revised requirements. The study demonstrates that the six-satellite 24-h MEO system can provide a suitable solution, which is also beneficial from the point of view of ionizing radiation and image acquisition geometry. Among the HEO systems, the 16-h HEO has some advantages relative to other HEO systems from the point of view of spatial coverage and space radiation.

A Review of Multiple Techniques for Obtaining Effective Satellite Data Over the Arctic Region

“…The study demonstrates that the orbit's altitude has an effect on coverage as well; the higher the altitude, the wider the coverage, albeit this effect is nonlinear and eventually reaches saturation [5].…”

“…Like GEO satellites, this orbit provides excellent imaging capabilities over the polar areas, however this is frequently at the expense of fluctuating altitude and speed in comparison to other orbit satellites [4].The HEO constellation benefits from being within the sheet or within the planes with the crucial inclination of 63.4358°, which reduces orbit maintenance costs related to drift. This drift limits the coverage of high-latitude regions by moving the apogee to a lower latitude over time [5]. The final visual representation of an elliptical orbit and the list of Keplerian orbital components are shown in Fig.…”

“…The vernal equinox point is the focal point of axis x. The apogee point is the point that is farthest from the centre of the earth, while the perigee point is the point that is closest to it.The angle 'i' is known as the orbit inclination [5] and is the angle between the sheets and the equatorial plane.…”

“…For satellites travelling on circular orbits, or with eccentricity, the dwelling duration over the polar zone is directly proportional to the angular size of the arc enclosing the segment of the orbit located inside the area of interest [5]. If the orbit's eccentricity rises, a greater percentage of the satellite's time will be spent over the poles [5]. One can approximate the orbit by thinking of it as an ellipse.…”

The Atmospheric Imaging Mission for Northern Regions: AIM-North

“…Since GEO satellites are stationed at a fixed longitude over the equator and synchronized with Earth's rotation, they have the ability to view within a region defined by some viewing zenith angle (VZA) limit. VZA limits differ for the retrieval of different constituents, and can range from $55 to 70 (Trishchenko et al, 2019a). For typical a VZA limit of 62 , regions poleward of $48-54 N/S (depending on longitude) are out of range.…”