Low-orbit satellite grouping of the system for monitoring geodesic parameters of the Earth and the direction of its development

Спутниковые миссии наряду с наземными геодезическими сетями различных космических технологий являются второй важной составляющей российского сегмента системы контроля геодезических параметров Земли (ГПЗ). Спутники имеют неоспоримое преимущество в том, что они непрерывно собирают однородные данные над большими частями земной поверхности. Они позволяют сбор данных, которые не могут быть зарегистрированы на поверхности Земли. Такие спутники в наше время оборудованы множеством датчиков, контролирующих поверхности суши, океана и льда, а также гравитационное поле Земли и его временные изменения. Потенциал и влияние спутниковых миссий для наблюдений Земли значительно возрастут в связи с тем, что: (1) будут запускаться все больше и больше спутниковых созвездий, вместо отдельных спутников, увеличивая тем самым временное и пространственное разрешение получаемых данных; (2) спутники будут летать в «формированиях», образуя большие наблюдательные приборы, состоящие из датчиков, расположенных на нескольких спутниках. В работе автор, с учетом рекомендаций международного геодезического сообщества, предлагает набор низкоорбитальных спутниковых миссий различных направлений, необходимых для полноценного функционирования системы контроля ГПЗ, и рассматривает направления развития данных миссий. Satellite missions, along with ground-based geodesic networks of various space technologies, will be the second important component of the Russian segment of the system for monitoring geodesic parameters of the Earth (GPE). Satellites have the undeniable advantage of continuously collecting uniform data over large parts of the Earth’s surface. They allow the collection of data that cannot be registered on the Earth’s surface. Such satellites are now equipped with a variety of sensors that monitor the surface of land, ocean and ice, as well as the Earth’s gravitational field and its temporal changes. The potential and impact of satellite missions for Earth observations will increase significantly as: (1) more and more satellite constellations will be launched, instead of individual satellites, thereby increasing the temporal and spatial resolution of the data received; (2) satellites will fly in “formations”, forming large observation instruments consisting of sensors located on several satellites. In this article the author taking into account the international geodetic community recommendations proposes a set of low-orbit satellite missions to various areas, necessary for proper operation of the system for monitoring GPE, and the directions of development of these missions are considered.

HISEA-1: The First C-Band SAR Miniaturized Satellite for Ocean and Coastal Observation

On 22 December 2020, HISEA-1, the first C-band SAR small satellite for ocean remote sensing, was launched from the coastal Wenchang launch site. Though small in weight, the images it produced have a high spatial resolution of 1 m and a large observation width of 100 km. The first batch of images obtained within the first week after the launch confirmed the rich information in the data, including sea ice, wind, wave, rip currents, vortexes, ships, and oil film on the sea, as well as landmark buildings. Furthermore, geometric characteristics of sea ice, wind vector, ocean wave parameter, 3D features of buildings, and some air-sea interface phenomena in dark spots could also be detected after relevant processing. All these indicate that HISEA-1 could be a reliable, remarkable, and powerful instrument for observing oceans and lands.

Estimation of precision of determination of the Yarkovsky effect parameter based on real and model asteroid observations

The paper presents the results of assessment definition precision of the Yarkovsky effect parameter A 2 for asteroids with small perihelion distances, known on epoch January 2021. It is shown that the observation interval has a significant effect on the precision of A 2. As the interval increases, the root mean square error of the parameter decreases. For asteroids (3200) Phaethon and (137924) 2000 BD19 with a large observation interval, an experiment was carried out to reduce the number of real observations. A decrease of the interval and number of observations leads to a loss in the precision of the parameter being determined. Modeling observations based on real ones with an increase in their precision showed that the root mean square error of the A 2 parameter decreases in proportion to the increase in the observation precision. The increase of interval due to model observations confirmed the conclusion about the inverse dependence of the A 2 uncertainty from number and interval of observations.

Angular Dependence of Ionoluminescence for Silica Case

The paper deals with angular dependence of ionoluminescence from transparent glossy silica samples. We measured silica ionoluminescence spectra at wavelength range of 400–700 nm for different projectiles (H1+, H2+, He+ 210 and 420 keV) and registered two most common intensive emission peaks (blue with a maximum at 456 nm and red one at 645 nm). To study luminescent angular dependence, the behavior of the blue peak maximum as a function of observation angle in the range of 0–70° was examined, namely, the indicatrix at the wavelength of 456 nm was found. The intensity corresponding to ionoluminescent indicatrices were found to be higher with respect to values from Lambertian angular distribution reaching approximately 20 % at large observation angles. We also calculated angular distribution of light above the sample surface taking into account refraction and reflection at the solid-ambient interface. The results obtained were in a good agreement with silica ionoluminescence experimental data for the average indicatrix curve. The latter indicates that the model assumption (luminescent light generated by fast ions within silica is unpolarized and isotropic) is correct. It was demonstrated that geometry of the experiment is very important, i.e., considering the light collected by the measuring system in a certain solid angle, one has to take into account that mutual arrangement of the sample and detector can distort angular distribution. The refraction at the border between a sample and vacuum (or air) strongly influences the luminescent light angular distribution.

UAV-Based Gigapixel Panoramic Image Acquisition Planning with Ray Casting-Based Overlap Constraints

Panoramic imaging is information-rich, low-cost, and effective. In panoramic image acquisition, unmanned aerial vehicles (UAVs) have a natural advantage that owes to their flexibility and relatively large observation ranges. Using a panoramic gimbal and a single camera may be the most common means of capturing gigapixel panoramas. In order to manage the constraints of UAV power and facilitate the use of a variety of camera lenses, an effective and flexible method for planning UAV gigapixel panorama acquisitions is required. To address this need, a panoramic image acquisition planning method is proposed in this paper. The method defines image overlaps via a ray casting procedure and then generates an acquisition plan according to the constraints of horizontal and vertical overlap thresholds. This method ensures the completeness of the panorama by maintaining the overlap between adjacent images. Two experiments, including simulated and field cases, were performed to evaluate the proposed method through comparisons with an existing panorama acquisition plan. Results showed that the proposed method can capture complete panoramas with fewer images.

THE SINGLE CURRENCY FOR ISLAMIC NATIONS: DO HETEROGENEITIES MATTER?

The purpose of this study is to assess the readiness of 44 OIC member countries to form a currency union and to test whether the Optimum Currency Area (OCA) criteria remain relevant to a large region like the OIC. Large geographic size is subject to socio-economic and geographic disparities. This study employs the OCA-index to estimate the degree of readiness of the OIC to form a currency union. Five selected criteria –business cycle synchronization, trade openness, inflation similarity, the size of the economy, and distance – were employed to determine the OCA using Ordinary Least Squares regression. The findings of this study estimate that 63 percent of pairs of countries in the OIC are ready to form a currency union. The selected OCA’s criteria present the best-fit variable in explaining the OCA for the OIC. This paper verifies that economic and geographic heterogeneities are not the main obstacle to forming a currency union. This study provides an important contribution to the theory of OCA primarily in clarifying the application of the OCA conditions in a large observation like the OIC, which comprises many countries and many blocs.

Direct Position Determination of Coherent Pulse Trains Based on Doppler and Doppler Rate

Direct Position Determination (DPD) of coherent pulse trains using a single moving sensor is considered in this paper. Note that when a large observation window and relative maneuvering course between emitter and receiver both exist, the localization accuracy of Doppler frequency shift only based DPD will decline because of the noticeable Doppler frequency shift variations. To circumvent this problem, a Doppler frequency shift and Doppler rate based DPD approach using a single moving sensor is proposed in this paper. First, the signal model of the intercepted coherent pulse trains is established where the Doppler rate is taken into consideration. Then, the Maximum Likelihood based DPD cost function is given, and the Cramer–Rao lower bound (CRLB) on localization is derived whereafter. At last, the Monto Carlo simulations demonstrate that in one exemplary scenario the Doppler frequency shift variations are noticeable with a large observation window and the proposed method has superior performance to the DPD, which is only based on the Doppler frequency shift.