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Home , Highly elliptical orbit, Molniya orbit, Tundra orbit

Multiple-Apogee Highly Elliptical for Continuous Meteorological Imaging of Regions Challenging the Classical 12-h Concept

by Alexander P. Trishchenko, Louis Garand, Larisa D. Trichtchenko, and Lidia V. Nikitina

DREAM: CONTINUOUS GLOBAL IMAGING. 1974. Since that time, the imaging technology has Satellite observations have transformed our percep- improved substantially. The Advanced Baseline tion of the –atmosphere system since the first Imager (ABI) developed for the third generation of images of Earth from space were acquired in 1960. geostationary , such as the U.S. Geostation- Nevertheless, a satellite meteorologist’s dream to ary Operational Environmental Satellite (GOES-R) observe weather at any point and time over the globe and the Japanese Himawari 8 and 9 (Himawari 8 remains elusive. This capability would represent launched in October 2014) can provide uninter- a breakthrough for short- and long-term weather rupted scans of the full Earth disk every 5 min. forecasting and narrowing uncertainties in the Sectors of 1,000 × 1,000 km can be acquired with a knowledge of Earth’s climate through better sam- temporal resolution of 30 s. These refresh rates can pling of the diurnal cycle. Continuous observation be effectively considered as “continuous imaging,” would also be beneficial for improving the quality of but a significant part of the globe still does not ben- satellite-derived essential climate variables (ECV). efit from similar capabilities. To a large extent, continuous imaging is achieved over the tropics and midlatitudes from geostationary CHALLENGE: POLAR REGIONS. Polar regions (GEO) satellites that rotate around the Earth at the are frequently called “the weather kitchens of the altitude of about 36,000 km in the equatorial plane Earth's climate.” Indeed, they exert great influence with the same angular rate as the planet. The satel- on global weather and show increased sensitivity lite can observe continuously with elevation angle to climate change. do not al- higher than 20° above the horizon a large region low GEO-type imaging over the poles. The polar that extends from the up to 62° . regions are presently monitored from low Earth Meteorological imaging from GEO orbit started in orbiting (LEO) satellites circling around the Earth at altitudes between 600 km and 900 km with a period of rotation close to 100 min. Due to the na- ture of LEO observations, the imaging refresh rate AFFILIATIONS: Trishchenko—Canada Centre for Remote Sensing, is restricted by the and the width of Natural Resources Canada, Ottawa, Ontario, Canada; Garand— Atmospheric Science and Technology, Environment Canada, Quebec, image swath. The frequency of observations is also Canada; Trichtchenko and Nikitina—Canadian Space Weather a function of latitude. For example, achieving the Forecast Centre, Natural Resources Canada, Ottawa, Ontario, image refresh rate of 15(10) min at 60° latitude circle Canada would require 23(34) polar LEO meteorological CORRESPONDING AUTHOR: Alexander P. Trishchenko, Canada satellites with orbital and imaging characteristics Centre for Remote Sensing, Natural Resources Canada, 560 similar to the Joint Polar Satellite System (JPSS). Rochester Str., Ottawa, ON K1A 0E4, Canada These numbers are prohibitively large to achieve E-mail: [email protected] the goal of GEO-like imaging at high from DOI:10.1175/BAMS-D-14-00251.1 LEO systems; therefore an alternative solution is required.

PB | JANUARY 2016 AMERICAN METEOROLOGICAL SOCIETY JANUARY 2016 | 19 Unauthenticated | Downloaded 09/29/21 09:14 PM UTC : CAPABILITIES AND DRAW- protons. The Molniya orbit crosses the proton radia- BACKS. Quasigeostationary coverage of polar tion belts at the region of maximum concentration of regions can be achieved from satellites in a highly energetic protons with energies up to several hundred elliptical orbit (HEO). The eccentricity of the HEO MeV. As an alternative, the 16-h three apogee (TAP) orbits is high by definition, and the satellite, in ac- HEO orbit was proposed, providing similar polar cordance with Kepler’s second law, spends most of the coverage as the Molniya HEO system while minimiz- time in the vicinity of apogee (i.e., the farthest point ing the proton ionizing hazards. The TAP orbit has a from the Earth’s surface). If the orbit altitude is high with three apogee points repeatable over enough, and the orbit is oriented in such a way that two days. The constellation of two satellites in TAP the apogee is located over one of the two polar regions, orbit still repeats the ground track in 24 h. then a combination of only two HEO satellites can The Molniya HEO orbit was suggested for meteo- maintain a continuous view of the entire polar zone. rological imaging in 1990, but has never been used When satellite A leaves the optimal viewing zone and operationally for that purpose. A new wave of interest heads toward the perigee (i.e., the closest point to the in HEO satellite systems started a few years ago, when Earth’s surface), satellite B rises over the region to the scale of climate change happening in the Arctic maintain the complete circumpolar region in sight. polar region and the economic opportunities it may Interestingly, there are periods of several hours per open became evident. Recognizing the importance day of coincident (i.e., stereo-like) imaging from the and potential of the HEO system for polar observa- two satellites over most of the circumpolar area. Such tions, the World Meteorological Organization (WMO) a system could provide meteorological imaging and created the International Geostationary Laboratory communication capacity similar to GEO, but focused for (IGEOLAB HEO) Focus on the polar region. Two pairs of HEO satellites (i.e., Group to coordinate international efforts in this field, a total of four satellites) would be required to insure and included the HEO concept in the most recent continuous coverage of both poles. WMO implementation plan for the evolution of the The first HEO satellite system with period of Global Observing System. rotation equal to 12 h and called Molniya was imple- mented for communication purposes in 1965. It is established that a two-satellite Molniya HEO constel- lation can achieve continuous coverage of the polar region 58°–90°N with a viewing zenith angle (VZA) less than 70°. Another HEO system—with a 24-h pe- riod—called Tundra is currently used by the satellite Sirius XM Radio service operating in North America. Both orbits, 12-h Molniya and 24-h Tundra, are launched with an orbit inclination equal to 63.4°. This value is called the critical inclination. It corresponds to zero rate of the apogee drift due to the second zonal harmonic of the Earth gravitational field, and insures a stable position of apogee over the polar zone. If the HEO orbit inclination differs from the critical value, then the apogee gradually drifts toward the equator. Orbital maneuvers are then required to maintain the intended orbit position. The farther orbit inclination is from the critical value, the more resources are re- quired to maintain the orbit. Therefore, it is highly recommended that the orbit inclination of the HEO Fig. 1. Ground track for (a) 12-h Molniya, (b) 16-h system be set at the critical value. TAP, and (c) 14-h and (d) 15-h two-satellite HEO A significant drawback associated with the 12-h constellations. Yellow and magenta colors denote Molniya orbit is the risk linked to hazardous levels ground tracks for each satellite in a two-satellite of ionizing radiation due to passing the Van Allen constellation flying in the same orbital plane and belts. The highest danger originates from high-energy separated by 180° phase angle.

20 | JANUARY 2016 AMERICAN METEOROLOGICAL SOCIETY JANUARY 2016 | 21 Unauthenticated | Downloaded 09/29/21 09:14 PM UTC Until now, most HEO studies designed to provide for the family of HEO orbits suitable for continuous services over polar areas were structured along the observations of the Earth’s polar regions. Analysis 12-h Molniya, 16-h TAP, and 24-h con- of ionizing radiation revealed the presence of a cepts that benefit from a ground track repeatable over local minimum in the region of orbital periods a 24-h period. A characteristic feature of these orbits between 14 h and 15 h. The total ionizing dose (TID) is the existence of a few (1, 2, or 3) standing apogee modeled via the Space Environment Information Sys- points as shown in Figs. 1a and 1b. tem (SPENVIS: www.spenvis.oma.be) at the reference A question comes to mind: Are the HEO orbital level of 50 krad over 15-yr period can be achieved with configurations previously developed for communica- 3.2 mm of aluminum shielding for the 14-h orbit and tion and surveillance applications also optimal for 3.3 mm for the 15-h orbit. This thickness of aluminum meteorological imaging of the polar regions? shielding is nearly 50% smaller than for the 12-h Mol- niya orbit. The total doses for protons are estimated to NOVEL SOLUTION: MULTIPLE-APOGEE HEO be 2–4 times smaller for the 14-h and 15-h orbits than SYSTEMS. We argue here that an HEO system with for the 12-h orbit. A reduced proton dose for MAP a small number of apogees is suboptimal for meteo- HEO systems is an important additional argument, as rological and climate applications. Indeed, with more proton radiation represents one of the most significant apogees, more evenly distributed imaging conditions risks to the HEO space mission. are obtained. This aspect is evident from Figs. 1c and Another important feature of the MAP configura- 1d, which shows the ground tracks for the 14-h and tions with orbital periods in the 14-h to 15-h range is 15-h HEO systems. The 14-h two-satellite HEO system that they can be at critical orbit inclination equal to has 24 apogees (12 for each satellite). The ground track 63.4°. It turns out that the orbit inclination for orbits repeats over a 7-day period. The 15-h two-satellite with period greater than 15 h needs to be increased HEO system has 16 apogees (8 for each satellite) above the critical value to achieve the required cov- repeated over a 5-day period. Due to a significantly erage of high latitudes within a reasonable imaging larger number of apogee points in comparison to 12-h, altitude range. This feature also favors 14-h and 16-h, and 24-h HEO orbits, we refer to these configu- 15-h orbits. Several other parameters of the MAP rations as multiple-apogee (MAP) HEO systems. This HEO orbits are presented in Table 1. The eccentric- is a first and major consideration, but there are more, ity ranges from 0.63 to 0.71, which insures sufficient as presented below. dwelling time around the apogee point located over The selection of MAP orbits presented in Table 1 the polar region. The imaging time is 16 h per day is based on our recent analysis of ionizing radiation over the polar zone, which is required to obtain

Table 1. Some features of the MAP HEO orbits.

Satellite Period * Repeat # orbits Imaging Perigee Eccentricity Imaging Altitude at latitude T (h) cycle per cycle time per (km) altitude midpoint range over (day) orbit range (km) (km) imaging period (deg)

14 7 12 9h20’ 2,131 0.711 44.5–63.4 14.25 19 32 9h30’ 2,830 0.691 42.9–63.4 14.4 3 5 9h36’ 3,247 0.679 41.9–63.4 14.5 29 45 9h40’ 3,525 0.672 41.3–63.4 26,600– ~39,900 14.67 11 18 9h46’40’’ 3,986 0.659 44,000 40.2–63.4 14.77 8 13 9h50’46’’ 4,268 0.651 39.6–63.4 14.90 18 29 9h55’52’’ 4,619 0.642 38.8–63.4 15 5 8 10 h 4,902 0.634 38.1–63.4

* Assuming sidereal day 24 h for simplicity. Apogee altitude H � 44,000 km for all orbits.

20 | JANUARY 2016 AMERICAN METEOROLOGICAL SOCIETY JANUARY 2016 | 21 Unauthenticated | Downloaded 09/29/21 09:14 PM UTC (continuous) coverage is achieved for a latitude range from the pole (90°) to slightly below 60°, while coverage of 50% is still achieved at 10° latitude, providing a valuable backup to all GEOs. As shown in Fig. 2b, the large number of apogees implies that the VZA ranges from zero to 70° for the entire region from the equator to 63.4° latitude. With a large number of apogees, any point in the circumpolar area can be continuously observed from multiple directions over the repeat period, thus dramatically increasing the diurnal cycle sampling. The distribution of viewing zenith angle versus relative azimuth and solar zenith angles is also quite diverse. The wide range of observational angles creates a unique capability for characterization of bidirectional reflectance properties of clouds and surface over polar latitudes. Fig. 2. Features of two-satellite 14-h HEO system for the This capacity is also superior to that from Northern Hemisphere. (a) Map of temporal coverage (%) over GEO in the region of HEO-GEO overlap. the repeat cycle. Arcs correspond to five GEO satellites equally Several other suitable MAP orbit spaced along the equator. (b) Distribution of minimum viewing configurations exist in addition to the zenith angle. 14-h and 15-h systems as shown in Table 1. They include, among others, uninterrupted coverage from a two-satellite system. the periods equal to 14.4 h and 14.77 h with 5 orbits The satellite altitude within the imaging period over a 3-day repeat cycle and 13 orbits over an 8-day ranges from 26,600 km to 44,000 km, with midpoint repeat cycle, correspondingly. In a two-satellite around 39,900 km, which is comparable to the GEO constellation for each hemisphere with satellite pairs height. The satellite latitude varies from 38.1° (15-h launched in the same orbital plane and separated by orbit) or 44.5° (14-h orbit) to 63.4° (i.e., equal to the 180° phase angle, the number of apogees increases orbit inclination), which is convenient for satellite two-fold. tracking from ground receiving stations located in mid- and high-latitude zones. The perigee heights VIEWING EARTH FROM HEO ORBIT: CHAL- range from 2,131 km to 4,902 km [i.e., significantly LENGES AND NEW OPPORTUNITIES. The HEO higher than the 12-h Molniya orbit value (~500 km)]. mission belongs to the GEO class of Earth Observing This is beneficial for reducing the atmospheric drag system due to a similar range of altitudes and image and collision avoidance with other satellites and space acquisition strategy (i.e., 2D scanning). The main debris in the near-Earth region densely populated at challenge in viewing the Earth from HEO orbit is a altitudes below 2,000 km. variable field of view due to continuously changing The spatial coverage achieved with 24 or 16 equally altitude. Several assessment studies were completed spaced apogees over the repeat cycle of 14-h and 15-h to evaluate the suitability of new-generation GEO orbits is very uniform (Fig. 2). This is an important imagers, like the ABI planned for GOES-R and the feature of the HEO system for climate applications, flexible combined imager (FCI) planned for Meteosat as it reduces biases in satellite-derived ECVs and Third Generation (MTG) satellites, to meet HEO other parameters caused by unequal distribution of imaging requirements. It was determined that the observational angles. The coverage shown in Fig. new-generation imagers are capable of acquiring 2a is obtained assuming a maximum VZA equal to imagery without gaps in HEO orbits while scanning 70° (i.e., minimum elevation angle of 20°). The 100% as fast as from GEO orbit. The realistic sensitivity

22 | JANUARY 2016 AMERICAN METEOROLOGICAL SOCIETY JANUARY 2016 | 23 Unauthenticated | Downloaded 09/29/21 09:14 PM UTC scenario analysis confirmed that the image geoloca- ACKNOWLEDGMENTS. This article has been as- tion accuracy will be similar to what is planned for signed the Earth Sciences Sector, Natural Resources Canada GEO. The effective image resolution collected from manuscript contribution number 20150112. The article is © HEO orbit varies with altitude; however, this is not Her Majesty the Queen in right of Canada 2015. perceived as a problem. The predetermined fixed grid map centered at the pole can be used for image remapping, similar to the GEO fixed grid. Normally, each satellite in a two-satellite HEO system should FOR FURTHER READING acquire imagery 16 h per day distributed symmetri- cally around the apogee point. This scenario creates Bojinski, S., M. Verstraete, T. C. Peterson, C. Richter, a unique opportunity for stereo imaging from two A. Simmons, and M. Zemp, 2014: The concept of satellites about 30% of the time. essential climate variables in support of climate re- Emerging technologies offer some new and unique search, applications, and policy. Bull. Amer. Meteor. applications, such as day-night imaging capacity cur- Soc., 95, 1431–1443, doi:10.1175/BAMS-D-13-00047.1. rently available from the Visible Infrared Imaging Garand, L., J. Feng, S. Heilliette, Y. Rochon, and A. P. Radiometer Suite (VIIRS) on the Suomi National Trishchenko, 2013: Assimilation of circumpolar Polar-orbiting Partnership (S-NPP) spacecraft. This is wind vectors derived from highly elliptical orbit im- important because of long periods of nighttime condi- agery: Impact assessment based on observing system tions lasting for several months over the polar zones. simulation experiments. J. Appl. Meteor. Climatol., 52, Selection of bands on new-generation GEO imagers 1891–1908, doi:10.1175/JAMC-D-12-0333.1. could be augmented with minor implications for the —, A. P. Trishchenko, L. D. Trichtchenko, and cost and technology to reflect the uniqueness of the R. Nassar, 2014: The Polar Communications and polar environment, such as a need for better snow/ice, Weather mission: Addressing remaining gaps in the fog, and haze retrievals. The HEO orbit is well suited Earth observing system. Phys. Canada, 70, 247–254. for observation of space weather (i.e., in situ magnetic Global Climate Observing System (GCOS), 2011: System- field and ionizing radiation measurements). Studies atic observation requirements for satellite-based data have also shown the unique capability of the HEO products for climate (2011 update). GCOS-154, World orbit to improve the carbon cycle characterization Meteorological Organization and Intergovernmental over the Arctic and boreal zone using HEO infrared Oceanographic Commission, 138 pp. [Available on- (IR) and visible-ultraviolet (VIS-UV) spectrometers, line at www.wmo.int/pages/prog/gcos/Publications as reported in provided references. /gcos-154.pdf.] Gultepe, I., and Coauthors, 2014: Ice fog in Arctic dur- SUMMARY. A novel type of highly elliptical orbits ing FRAM-ice fog project: Aviation and nowcasting termed as multiple-apogee (MAP) HEO systems with applications. Bull. Amer. Meteor. Soc., 95, 211–226, orbital periods between 14 h and 15 h is introduced. doi:10.1175/BAMS-D-11-00071.1. The MAP HEO two- for each Hollmann, R., and Coauthors, 2013: The ESA climate hemisphere is designed to achieve continuous GEO- change initiative: Satellite data records for essen- like imaging of the polar regions in an optimal way. tial climate variables. Bull. Amer. Meteor. Soc., 94, These systems can be launched at critical orbit inclina- 1541–1552, doi:10.1175/BAMS-D-11-00254.1. tion and correspond to a local minimum of ionizing Kidder, S. Q., and T. H. Vonder Haar, 1990: On the use radiation with a relatively small proton component. of satellites in Molniya orbits for meteorological These features simplify the process of orbit mainte- observation of middle and high latitudes. J. Atmos. nance, reduce radiation shielding requirements, and Oceanic Technol., 7, 517–522, doi:10.1175/1520 favor a longer lifetime of the mission. In comparison -0426(1990)007<0517:OTUOSI>2.0.CO;2. to conventional HEO systems with a few apogees, Lachance, R. L., and Coauthors, 2012: PCW/PHEOS- like the classical 12-h Molniya concept, a MAP HEO WCA: Quasi-geostationary Arctic measurements constellation with multiple apogees achieves a more for weather, climate, and air quality from highly uniform geometrical sampling, which reduces view eccentric orbits. Proc. SPIE, 8533, article #85330O, angle–dependent biases. These observational condi- doi:10.1117/12.974795. tions are beneficial for high-latitude meteorological Moreau, L., P. Dubois, F. Girard, F. Tanguay, and and climate applications. J. Giroux, 2012: Concept and technology development

22 | JANUARY 2016 AMERICAN METEOROLOGICAL SOCIETY JANUARY 2016 | 23 Unauthenticated | Downloaded 09/29/21 09:14 PM UTC for the multispectral imager of the Canadian polar communications and weather mission. Proc. SPIE, 8533, article # 85330N, doi:10.1117/12.974713. Nassar, R., C. E. Sioris, D. B. A. Jones, and J. C. McConnell, 2014: Satellite observations of CO2 from a highly elliptical orbit for studies of the Arctic and boreal carbon cycle. J. Geophys. Res., 119, 2654–2673. Puschell, J. J., D. Johnson, and D. S. Miller, S., 2014: Persistent observations of the Arctic from highly el- liptical orbits using multispectral, wide field of view day-night imagers. Proc. SPIE, 9223, article # 922304, doi:10.1117/12.2064912. Schmit, T. J., M. M. Gunshor, W. P. Menzel, J. Li, S. Bachmeier, and J. J. Gurka, 2005: Introducing the next-generation Advanced Baseline Imager (ABI) on GOES-R. Bull. Amer. Meteor. Soc., 86, 1079–1096, doi:10.1175/BAMS-86-8-1079. Trishchenko, A. P., and L. Garand, 2011: Spatial and temporal sampling of polar regions from two-satellite system on Molniya orbit. J. Atmos. Oceanic Technol., 28, 977–992, doi:10.1175/JTECH-D-10-05013.1. —, and —, 2012: Observing polar regions from space: Advantage of satellite system on highly elliptical orbit versus constellation of low Earth polar orbiters. Can. J. Rem. Sens., 38, 12–24, doi:10.5589/m12-009. —, —, and L. D. Trichtchenko, 2011: Three apogee 16-h highly elliptical orbit as optimal choice for continuous meteorological imaging of polar regions. J. Atmos. Oceanic Technol., 28, 1407–1422, doi:10.1175 /JTECH-D-11-00048.1. Trichtchenko, L. D., L. V. Nikitina, A. P. Trishchenko, and L. Garand, 2014: Highly elliptical orbits for Arctic observations: Assessment of ionizing radia- tion. J. Adv. Space Res., 54, 2398–2414, doi:10.1016/j .asr.2014.09.012. Vallado, D. A., 2007: Fundamentals of Astrodynamics and Applications. 3d ed. Microcosm Press/Springer, 1,055 pp. World Meteorological Organization (WMO), 2013: Implementation plan for the evolution of Global Observing Systems (EGOS-IP). Tech. Rep. 2013-4. 116 pp. [Available online at www.wmo.int/pages /prog/www/OSY/Publications/EGOS-IP-2025 /EGOS-IP-2025-en.pdf.]

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