A preliminary study of level 1A data processing of a low-low satellite to satellite tracking mission

With the Gravity Recovery and Climate Experiment {GRACE） mission as the prime example, an overview is given on the management and processing of Level IA data of a low-low satellite to satellite tracking mission. To illustrate the underlying principle and algorithm, a detailed study is made on the K-band ranging （KBR） assembly, which includes the measurement principles, modeling of noises, the generation of Level 1A data from that of Level 0 as well as Level IA to Level IB data processing.

Satellite Tracking of Post-nesting Migration of Green Turtles

During the period August 17-28, 2001, in collaboration with the Provincial Bureau of Oceanography & Fisheries of Guangdong and the South China Institute for Endangered Species, the South China Sea Institute of Oceanology, a CAS affiliate in the city of Guangzhou, conducted a sea turtle satellite tracking project at Haigui Bay (Fig. 1) in the vicinity of Gangkou Town, Huidong County, Guangdong Province.

An Experimental Biotelemetric Study Based on Satellite Tracking During Post-nesting Migrations of Green Turtles

A biotelemetry experiment is conducted to study the migrant behavior of green turtles (Chelonia mydas) in South China Sea and acquire the physical environment data. The method in use is to track the post nesting migrant routes of green turtles through the satellite linked transmitters attached on the back of turtles and the global satellite signal transmitting system of Argos. We obtained the positions of the post nesting migrant routes of three green turtles and environment data, which are important in conservation of green turtles and the research of physical oceanography. Based on the test, the concept, principle and method of biotelemetry are also introduced in this paper with a discussion of the further development of this technique and its applying prospection in future.

Wideband and high-gain BeiDou antenna with a sequential feed network for satellite tracking

BeiDou-3 navigation satellite system was officially opened in 2020.While bringing high-performance services to people around the world,the navigation system requires well-designed BeiDou antennas.In this paper,we propose a wideband circularly polarized high-performance BeiDou antenna.The antenna realizes wideband circularly polarized radiation through a four-port sequential feed network,and the phase imbalance of the feed network from 1.05 to 1.80 GHz is less than 7°.The manufactured antenna demonstrates a return loss of more than 13 dB and an axial ratio<3 dB over the entire global navigation satellite system(GNSS)frequency band.The right-handed circular polarization(RHCP)gain of the proposed antenna is greater than 4 dB in the GNSS low-frequency band and can reach more than 7.1 dB in the high-frequency band.Dimension of the proposed antenna is 120 mm×120 mm×20 mm,i.e.,0.54λo×0.54λo×0.09λo,whereλo is the wavelength of the center frequency.The proposed antenna connected to a GNSS receiver has tracked 12 BeiDou satellites with C/N0 ratios of GNSS signals greater than 30 dB.Such a high-performance antenna provides a basis for high-quality positioning services.

Tracking the Confiscated Green Sea Turtles in the South China Sea:Where Did They Come From?Where Will They Go?

The population of the green sea turtle(Chelonia mydas)is under decline,threatened by bycatch and illegal acquisition despite worldwide protection efforts.However,the confiscation of illegally acquired sea turtles could aid in tracking their origin and movement patterns,crucial for effective conservation strategies.Combining satellite tracking and genetic analysis offers an opportunity to investigate the relationship between the origins and migration directions of green sea turtles in the western Pacific.Here,we applied two methods to investigate the spatial ecology of 18 green turtles caught as bycatch in the South China Sea.Our results revealed the genetic origins and diverse movements of the turtles.Bayesian Mixed Stock Analysis(MSA)suggested that these turtles originated from the rookery of the Xisha Islands(49.6%),central Ryukyu(24.6%),NE Borneo(8%),and the Sulu Sea(5.2%),with other rookeries in meagre proportions(<2%each).Satellite tracking showed the ranges of their travel were smaller than the whole contributed rookery range,but diverse.The haplotype diversity of these turtles is high,and CmP19 stands out as both the most frequent and the most diverse haplotype in terms of swimming destinations.These results indicate that the South China Sea is likely an important transportation hub and mating spot for green turtles.Our findings provided evidence for the rehabilitation of these green turtles in the wild and illustrated the complexity of movement during the green turtle’s life history,and the“mixed backgrounds”of the green turtles also highlight the need for joint conservation efforts of neighbouring countries in the South China Sea.

Application of geovisual analytics to modelling the movements of ruminants in the rural landscape using satellite tracking data

Geovisual analytics provides a framework for the development of decision support tools for landscape design,analysis and optimisation.An important application is modelling the spatial-temporal movements of ruminants and their grazing behaviour using global positioning system(GPS)collar units.This study describes the mapping and analysis of spatial distributions of animal waste products(which correlate with farm nitrogen[N]emissions)and also determination of animal feeding preferences(which correlate with animal welfare and production).Segmentation of local regions of animal N emissions provides support in meeting targets for local and international N leaching and greenhouse gas emissions.An agent-based model was used for prescreening in order to gain insights into the clustering behaviour of sheep during feeding activities.Subsequent spatial analysis demonstrated that livestock excreta are not always randomly located,but concentrated around highly localised animal gathering points,separated by the nature of the excretion.In a separate study,the statistical significance of feeding choices was determined by testing a null hypothesis on animal boundary transitions between adjacent pastures using the binomial approximation.The analysis also included compensation for the precision of the GPS sensor,which produced a fuzzy decision boundary.

Activity Pattern and Habitat Use of Shorebirds in an Artificial Wetland Complex:A Case Study of Breeding Pied Avocet in the Yellow River Delta,China

With the loss of substantial natural wetlands in coastal zones,artificial wetlands provide alternative habitats for many shorebirds.Scientific management of artificial wetlands used by shorebirds plays an important role in maintaining the stability of shorebird population.Satellite tracking technique can obtain high-precision location information of individuals day and night,providing a good technical support for the study of quantitative relationship between waterfowls and their habitats.In this study,satellite tracking method,Remote Sensing(RS)and Geographic Information System(GIS)technology were used to analyze the activity pattern and habitat utilization characteristics of Pied Avocet during breeding period in an artificial wetland complex in the Yellow River Delta(YRD),China.The results showed that the breeding Pied Avocets had a small range of activity,with a total core and main home range of 33.10 km^(2) and 216.30 km^(2),respectively.This species tended to forage in the pond and salt pan during the day and night,respectively,with an unfixed staying time in the breeding ground.The distance between breeding ground and feeding ground was less than 6 km.It is emphasized that in addition to improving the conditions of the remaining natural habitats,effective managing artificial habitats is a priority for shorebird conservation.This research could provide reference for the management of artificial wetlands in coastal zones and supply technique support for the protection of shorebirds and their habitats,and alleviate human-bird conflicts and sustainable development of coastal zones.

A Novel Roll Compensation Method for Two-Axis Transportable Satellite Antennas

Two-axis transportable satellite antennas(TATSAs) have been widely adopted owing to its simple structure and low cost. However, by searching in a wide range, it will take a very long searching time. Under extreme conditions, it will even fail to work. In this paper, we propose a novel roll compensation(RC) method for the low-cost TATSAs to achieve faster tracking even if when the antenna has no azimuth sensor. By analyzing the influence of roll axis on the system performance, details of the compensation method are derived. Simulation and measurement results indicate that the proposed RC method can effectively reduce the initial searching time for satellite communication. In addition, tracking along with the ellipse path with the RC method provides the highest tracking efficiency.

Zenith Pass Problem of Inter-satellite Linkage Antenna Based on Program Guidance Method

While adopting an elevation-over-azimuth architecture by an inter-satellite linkage antenna of a user satellite, a zenith pass problem always occurs when the antenna is tracing the tracking and data relay satellite （TDRS）. This paper deals with this problem by way of, firstly, introducing movement laws of the inter-satellite linkage to predict the movement of the user satellite antenna followed by analyzing the potential pass moment and the actual one of the zenith pass in detail. A number of specific orbit altitudes for the user satellite that can remove the blindness zone are obtained. Finally, on the base of the predicted results from the movement laws of the inter-satellite linkage, the zenith pass tracing strategies for the user satellite antenna are designed under the program guidance using a trajectory preprocessor. Simulations have confirmed the reasonability and feasibility of the strategies in dealing with the zenith pass problem.

Comparison between several satellite constellation schemes for MEO-TDRSS of China

The satellite constellation classes, which are suitable for the medium earth orbit tracking and data relay satellite system （MEO-TDRSS） of China, are investigated. On the basis of the functionality and the traffic distribution characteristic of MEO-TDRSS, the coverage performance and inter-satellite link properties of four different constellation schemes are compared by simulations. Simulation results indicate that the rosette and common-track constellations, whose satellites are distributed on the celestial sphere more uniformly, are appropriate for the implementation of MEO-TDRSS of China.

A Power Reduction Method for Pilot Channel of LEO Satellite Based on Dynamic Compensation

Since the lower power requirement of code division multiple access(CDMA) than that of other multiple access, the CDMA technology is suitable to be used in low earth orbit(LEO) satellite communication system whose space power is limited due to the small size of satellite. The pilot channel of CDMA technology is very important for earth mobile station(EMS) in LEO system to recover carrier and code, but the power requirement of pilot channel is very higher than that of other channels. In this paper, a power reduction method for pilot channel is proposed. By the new method, the power of pilot channel transmitted from LEO satellite is reduced to a lower level. For improving the signal to noise ratio(SNR) of pilot channel with lower power, coherent integration is employed in EMS at the pre-processing stage. Considering the high dynamic situation of LEO satellite, the long period of time for integration will deteriorate the receiving performance of EMS, therefore, a dynamic compensation module is added to carrier tracking loop against the high dynamic. Meanwhile, the transfer function of the new tracking loop and the condition for steadystate zero error are deduced. Numerical examples are provided to demonstrate effectiveness of the proposed approach.

Evaluating Behavioural Modelling Predictions in the Blue Shark (Prionace glauca) Enables Greater Insight on Habitat Use from Location only Argos Data

The relationship between habitat and behaviour provides important information for species management.For large,free roaming,marine animals satellite tags provide high resolution information on movement,but such datasets are restricted due to cost.Extracting additional biologically important information from these data would increase utilisation and value.Several modelling approaches have been developed to identify behavioural states in tracking data.The objective of this study was to evaluate a behavioural state prediction model for blue shark(Prionace glauca)ARGOS surface location-only data.The novel nature of the six SPLASH satellite tags used enabled behavioural events to be identified in blue shark dive data and accurately mapped spatio-temporally along respective surface location-only tracks.Behavioural states modelled along the six surface location-only tracks were then tested against observed behavioural events to evaluate the model’s accuracy.Results showed that the Behavioural Change Point Analysis(BCPA)model augmented with K means clustering analysis performed well for predicting foraging behaviour(correct 86%of the time).Prediction accuracy was lower for searching(52%)and travelling(63%)behaviour,likely related to the numerical dominance of foraging events in dive data.The model’s validation for predicting foraging behaviour justified its application to nine additional surface location-only(SPOT tag)tracks,substantially increasing the utilisation of expensive and rare data.Results enabled the critical behavioural state of foraging,to be mapped throughout the entire home range of blue sharks,allowing drivers of critical habitat to be investigated.This validation strengthens the use of such modelling to interpret historic and future datasets,for blue sharks but also other species,contributing to conservational management.

Hierarchical Disturbance Propagation Mechanism and Improved Contract Net Protocol for Satellite TT&C Resource Dynamic Scheduling

The practical engineering of satellite tracking telemetry and command(TT&C)is often disturbed by unpredictable external factors,including the temporary rise in a significant quantity of satellite TT&C tasks,temporary failures and failures of some TT&C resources,and so on.To improve the adaptability and robustness of satellite TT&C systems when faced with uncertain dynamic disturbances,a hierarchical disturbance propagation mechanism and an improved contract network dynamic scheduling method for satellite TT&C resources were designed to address the dynamic scheduling problem of satellite TT&C resources.Firstly,the characteristics of the dynamic scheduling problem of satellite TT&C resources are analyzed,and a mathematical model is established with the weighted optimization objectives of maximizing the revenue from task completion and minimizing the degree of plan disturbance.Then,a bottom-up distributed dynamic collaborative scheduling framework for satellite TT&C resources is proposed,which includes a task layer,a resource layer,a central internal collaboration layer,and a central external collaboration layer.Dynamic disturbances are propagated layer by layer from the task layer to the central external collaboration layer in a bottom-up manner,using efficient heuristic strategies in the task layer and the resource layer,respectively.We use improved contract network algorithms in the center internal collaboration layer and the center external collaboration layer,the original scheduling plan is quickly adjusted to minimize the impact of disturbances while effectively completing dynamic task requirements.Finally,a large number of simulation experiments were carried out and compared with various comparative algorithms.The results show that the proposed algorithm can effectively improve the solution effect of satellite TT&C resource dynamic scheduling problems,and has good application prospects.

Detecting the non-breeding region and migration route of Whimbrels(Numenius phaeopus rogachevae)in the East Asian–Australasian Flyway

Determining the migration routes and connections of migratory birds at the population level helps clarify intraspecific differences in migration.Five subspecies have been recognized in the Whimbrel(Numenius phaeopus)in Eurasia.Ssp.rogachevae is the most recently described subspecies.It breeds in Central Siberia,while its non-breeding region and migration routes are still unclear.We tracked the migration of Eurasian Whimbrels captured at three non-breeding sites(Moreton Bay in east coast of Australia,Roebuck Bay in Northwest Australia and Sungei Buloh Wetland in Singapore)and two migration stopover sites(Chongming Dongtan and Mai Po Wetland in China).We determined the breeding sites and inferred the subspecies of the tagged birds in the East Asian–Australasian Flyway(EAAF)based on the known breeding distribution of each subspecies.Of the 30 tagged birds,6 and 21 birds bred in the breeding range of ssp.rogachevae and variegatus,respectively;one bred in the presumed transition area between the breeding range of ssp.phaeopus and rogachevae,and two bred in the region between the breeding range of ssp.rogachevae and variegatus.The birds that bred in the ssp.rogachevae breeding range spent their non-breeding season in the northern Sumatra,Singapore,East Java and Northwest Australia and mainly stopped over along China's coasts during migration.None of our birds bred in the exclusive breeding range of the phaeopus subspecies.Previous studies have predicted that rogachevae whimbrels migrate along the Central Asian Flyway and spend the non-breeding season in West India and East Africa.We found that at least some rogachevae whimbrels migrate along the EAAF and spend the non-breeding season in Southeast Asia and Australia.The ssp.phaeopus is at best sparsely distributed in the EAAF in the west region,or possibly does not occur at all.

Autumn migration routes of fledgling Chinese Egrets(Egretta eulophotes)in Northeast China and their implications for conservation

The Chinese Egret(Egretta eulophotes)is a globally threatened bird species living on the coast and islands of Liaoning,northeastern China,mainly in summer.To further protect the breeding population of Chinese Egrets,it is important to understand the current protection status of their distribution sites at pre-migration period and migration routes.Thirty-three individuals were tagged with satellite transmitters at Fantuo Island in Changhai and Xingren Island in Zhuanghe,Liaoning Province,northeastern China,in July of 2016,2017,and 2018,to identify important distribution sites during the pre-migration period,as well as detailed migration routes.The results showed that coastal mudflats in Liaoning and the west coast of North Korea were important feeding and roosting sites for fledgling Chinese Egrets from August to September.The home range sizes in August were significantly larger than in September.The eastern coast from Shandong to Guangdong,as well as Taiwan,China,and Manila Bay and Galileo Islands in the Philippines,were important stopover sites during fall migration.Specifically,we found that the egrets’autumn migration could be divided into four routes,i.e.,sea-crossing migration(SCM),coastal migration(CM),inland migration(IM),and mixed migration(MM).The migration distance,timing,speed,and straightness of the four routes also differed.The SCM routes were the straightest,and had the fastest migration speed and shortest travel time,while the IM routes had the lowest straightness and speed,and the longest duration.Manila Bay and Bohol Island in the Philippines,the west coast of Tanintharyi in Myanmar,and the Zengwun River Estuary in Taiwan,China,were wintering sites.Our findings on the key distribution sites along pre-migration and fall migration routes,including some stopover sites,have important implications for the conservation of and global action plan development for the vulnerable Chinese Egret.

Feedforward attitude control for a TDRS with mobile antennas

In this paper, feedforward attitude control law for a Tracking and Data Relay Satellite （TDRS） with mobile antennas is proposed. To track or point the target spacecraft with median/law orbit, the large mobile antennas have to move in a wide range. The movement of such mobile antennas disturbs the satellite attitude conscquently. Conventionally, the main body of thc satellitc and the mobile antennas are controlled independently. The proposed controller first estimates the angular momentum which the mobile antennas will produce based on tiLe momentum conservation equation. Next, it computes the desired velocity of reaction wheels to compensate the disturbance due to the antenna motion. It then adds the errnr of the wheels＇ velocity between a desired one and a current value as a feedforward signal to the control system. The proposed controller is demonstrated using a mathematical simulation, of which these results coincide well with analytical results.

Dispersal patterns of Reeves's pheasant based on genetic and behavioral evidence

Dispersal is an important life history trait that plays a crucial role in avoiding inbreeding.Uncovering the dispersal pattern of a threatened species facilitates conservation efforts.Most species of Galliformes are forest-dwelling terrestrial birds with a weak dispersal ability and high conservation priorities.However,little is known about the dispersal behavior and dispersal pattern of Galliformes species such as Reeves's pheasant Syrmaticus reevesi,a globally vulnerable species endemic to China.Here,we integrated behavioral and genetic analyses to inves-tigate the dispersal pattern of Reeves's pheasant.Our results revealed that both females and males would disperse,although the overall dispersal pattern was more likely to be male-biased.Reeves's pheasant population had a low level of genetic diversity and a mild level of inbreeding.Speculation low genetic diversity was resulted from fragmented habitat,and male-biased dispersal may reduce the opportunity of inbreeding.Our research indicated that sex-biased dispersal patterns may be a behavioral mechanism adopted by wildlife to avoid inbreeding inafragmented habitat.

Type synthesis of 2-DoF rotational parallel mechanisms actuating the inter-satellite link antenna

This paper focuses on the type synthesis of two degree-of-freedom(2-DoF) rotational parallel mechanisms(RPMs) that would be applied as mechanisms actuating the inter-satellite link antenna. Based upon Lie group theory, two steps are necessary to synthesize 2-DoF RPMs except describing the continuous desired motions of the moving platform. They are respectively generation of required open-loop limbs between the fixed base and the moving platform and definition of assembly principles for these limbs. Firstly, all available displacement subgroups or submanifolds are obtained readily according to that the continuous motion of the moving platform is the intersection of those of all open-loop limbs. These subgroups or submanifolds are used to generate all the topology structures of limbs. By describing the characteristics of the displacement subgroups and submanifolds intuitively through employing simple geometrical symbols, their intersection and union operations can be carried out easily. Based on this, the assembly principles of two types are defined to synthesize all 2-DoF RPMs using obtained limbs. Finally, two novel categories of 2-DoF RPMs are provided by introducing a circular track and an articulated rotating platform,respectively. This work can lay the foundations for analysis and optimal design of 2-DoF RPMs that actuate the inter-satellite link antenna.

Individual repeatability in timing and spatial flexibility of migration routes of trans-Saharan migratory raptors

Satellite-tracking technology has allowed scientists to make a quantum leap in the field of migration ecology. Nowadays, the basic description of migratory routes of many species of birds has been reported. However, the investigation of bird migration at individual level （i.e. repeatability in migratory routes and timing） still remains seldom explored. Here, we investigated repeated migratory trips of a trans-Saharan endangered migratory raptor, the Egyptian Vulture Neophron percnopterus, tracked by GPS satellite telemetry. We compared between- and within-individual variation in migratory routes and timing in order to assess the degree of repeatability （or conversely, the flexibility） in migration. To this end, we analysed a dataset of 48 trips （23 springs and 25 autumns） recorded for six adult birds during 2007-2013. Our results showed consistent migration timing at the individual level, both in spring and autumn. Interestingly, there was a high degree of flexibility in the routes followed by the same individual in different years, probably due to variations in meteorological conditions. Contrary to expectations of a faster migration in spring than in autumn owing to a time-minimization strategy for breeding, birds spent less time in autumn migration （13 ± 2 days, range = 9-18 d） than in spring migration （19 ± 3 days, range = 13-26 d）, which can be explained by differences in environmental con- ditions en route. Egyptian vultures showed a consistent clockwise loop migration through western Africa, following more easterly routes in autumn than in spring. Finally, our results provide supporting evidence of low phenotypic plasticity in timing of migration （i.e. strong endogenous control of migration） and high flexibility in routes [Current Zoology 60 （5）： 642-652, 2014].

Time and energy minimization strategy codetermine the loop migration of demoiselle cranes around the Himalayas

Tens of thousands of demoiselle cranes’crossing the Himalayas to the Indian subcontinent have been reported for decades,but their exact spring migration route remained a mystery until our previous study found they made a detour in spring along the western edge of the Himalayas and crossed the Mongolian Plateau to their breeding areas based on satellite telemetry of 3 birds.To corroborate the loop migration pattern and explore whether demoiselle crane’s loop migration route is shaped by time-and energy-minimization strategies in spring and autumn and how the temporal and spatial variation of environmental conditions contribute to crane’s selection of migration routes,we tracked 11 satellite-tagged demoiselle cranes from their breeding area in China and Russia,simulated 2 pseudo migration routes,and then compared the environmental conditions,time,and energy cost between true and pseudo routes in the same season.Results show that demoiselles’spring migration obeyed time-minimization hypothesis,avoiding the colder Qinghai-Tibet Plateau,benefited by abundant food and higher thermal and orographic uplift along the route;autumn migration follows energy-minimization hypothesis with the shorter route.Our research will contribute to uncover the mechanical reasons why demoiselle crane avoids crossing the giant barrier of the Himalayas in spring,and shapes a loop migration route.