Processing methodology for the ITS_LIVE Sentinel-1 ice velocity product

The NASA MEaSUREs Inter-mission Time Series of Land Ice Velocity and Elevation (ITS_LIVE) project seeks to accelerate understanding of critical glaciers and ice sheet processes by providing researchers with global, low-latency, comprehensive and state-of-the-art records of surface velocities and elevations as observed from space. Here we describe the image-pair ice velocity product and processing methodology for ESA Sentinel-1 radar data. We demonstrate improvements to the core processing algorithm for dense offset tracking, “autoRIFT”, that provides finer resolution and higher accuracy data products with improved computational efficiency when compared to earlier versions. A novel calibration is applied to the data to correct for Sentinel-1A/B subswath- and full swath-dependent geolocation errors caused by systematic issues with the instruments. Sentinel-1’s C-band images are affected by variations in the total electron content of the ionosphere that results in large velocity errors in the azimuth (along-track) direction. To reduce these effects slant-range (line-of-sight or LOS) velocities are used and accompanied by LOS parameters that support map coordinate (x/y) velocity inversion from ascending and descending slant-range offset measurements, as derived from 2 image-pairs. The described product and methods comprise the MEaSUREs ITS_LIVE Sentinel-1 Image-Pair Glacier and Ice Sheet Surface Velocities: Version 2 (https://its-live.jpl.nasa.gov).

INDICATORS OF SA-19 “GRISON” ANTI-AIRCRAFT GUN MISSILE SYSTEM EFFICIENCY WHEN FIRING AT NONTYPICAL TARGETS OF THE ROCKET AND ARTILLERY WEAPONS

In modern conditions of combat use the SA-19 “Grison” anti-aircraft gun missile system fires at small targets (drones) and typical targets (helicopters and attack aircraft), so a number of problems arise. In particular, they include: finding the value of the probabilities of hitting the target with n shots and one shot; assessing the effectiveness of the SA-19 “Grison” platoon‟s concentrated fire on a single target; estimating errors of missile guidance and warhead detonation system; estimating the values of conditional probabilities of hitting a target with a single missile, depending on the value of particular mishit. When calculating the slant range to the far edge of the SA-19 “Grison” weapon's kill zone under different conditions of use, factors that reduce these ranges should be taken into account. An analysis of the main studies and publications presented in [1-9] does not make it possible to determine the performance of missile and artillery weapons in shooting at small-size targets. This literature provides general approaches to solving this problem. The purpose of this article is to develop a model for calculating the values of conditional probabilities of destruction of small targets, to form the best options for repelling an enemy‟s air strike, as well as to justify the general directions of improvement of weapon‟s elements.

Method and algorithm for determining the geographic coordinates of ground objects from an unmanned aerial vehicle

Introduction: As practice shows, the accuracy of determining the coordinates of objects is influenced by many factors associated with the presence of errors in measuring the angular coordinates of the optical system, the distance to the object and the presence of an inhomogeneous terrain. Purpose: Improving the accuracy of determining the geographic coordinates of ground objects from an unmanned aerial vehicle. Results: A method and an algorithm for determining geographic coordinates based on the use of a digital terrain model and optimization methods have been developed. The accuracy of calculating the coordinates of the object is increased by minimizing the error in measuring the declination angle, azimuth to the target and slant range. To confirm the analytical calculations, a field experiment was carried out with a car on the ground. At a considerable distance, at which the slant range was 900 m, several data freeze frames were taken. As a result of calculations, the geographical coordinates of the car were obtained in two ways (traditional and developed). Ultimately, the accuracy of calculating coordinates using the developed method is 4.8 times higher. Practical relevance: The method and algorithms for information processing proposed in the work will make it possible to create a number of hardware and software solutions for guidance and target designation systems.

The Ad Hoc Back-End of the BIRALET Radar to Measure Slant-Range and Doppler Shift of Resident Space Objects

Space debris is a term for all human-made objects orbiting the Earth or reentering the atmosphere. The population of space debris is continuously growing and it represents a potential issue for active satellites and spacecraft. New collisions and fragmentation could exponentially increase the amount of debris and so the level of risk represented by these objects. The principal technique used for the debris monitoring, in the Low Earth Orbit (LEO) between 200 km and 2000 km of altitude, is based on radar systems. The BIRALET system represents one of the main Italian radars involved in resident space objects observations. It is a bi-static radar, which operates in the P-band at 410–415 MHz, that uses the Sardinia Radio Telescope as receiver. In this paper, a detailed description of the new ad hoc back-end developed for the BIRALET radar, with the aim to perform slant-range and Doppler shift measurements, is presented. The new system was successfully tested in several validation measurement campaigns, the results of which are reported and discussed.

Moving Target Detection and Parameter Estimation via a Modified Imaging STAP with a Large Baseline in Multistatic GEO SAR

With the development trends of multistatic spaceborne synthetic aperture radar (SAR), geosynchronous SAR (GEO SAR) employing several formation-flying small satellites also has great potential for remote sensing. The small satellites can cooperate to acquire multi-channel data for moving target detection and parameter estimation in strong clutters. However, multistatic GEO SAR has large satellite spacing and a curved trajectory, which induce the near-field effects and channels out of alignment, respectively, bringing about challenges for the spatial adaptive processing. These problems produce a high-order term in the multi-channel slant range model, making the traditional model and adaptive processing method invalid. In this paper, to meet the requirement of SAR focusing, we firstly derive a fourth-order slant range model and a third-order path difference model for multistatic GEO SAR. Secondly, based on the derived model, the principle of stationary phase and series reversion method are utilized to derive the spatial steering vector for a moving target, which is a basis of spatial adaptive processing in the range-Doppler domain. Thirdly, the time-domain match filtering is constructed based on the fourth-order slant range model to image the moving target. Additionally, the moving targets are detected in the image domain. The motion parameter is estimated by iteratively maximizing the output signal to clutter and noise ratio (SCNR) through the range of possible target velocities. Finally, considering that the GEO SAR is still in development, the computer simulations are carried out to verify the effectiveness and evaluate the performance.

Interpretasi Objek Dasar Laut Berdasarkan Nilai Hambur Balik Menggunakan Instrumen Side Scan Sonar (Studi Kasus Pipa Pertamina di Balongan)

Side scan sonar merupakan instrumen single beam yang mampu menunjukkan gambar dua dimensional permukaan dasar laut dengan kondisi kontur, topografi dan target secara bersamaan. Teknologi ini merupakan penginderaan jauh akustik untuk pemetaan sedimen dan struktur dasar laut. Side scan sonar merekam energi gelombang akustik yang dipancarkan oleh hambur balik dasar laut sehingga mampu membedakan besar kecil partikel penyusun permukaan dasar laut. Pengaruh dari intensitas hambur balik tergantung pada tipe, magnitudo dan orientasi dari kekasaran dasar perairan yang dapat mendeskripsikan dasar laut. Penelitian ini bertujuan untuk memvisualisasikan dan menginterpretasikan hasil pengolahan data dari side scan sonar pada pendeteksian target yang berupa pipa diperairan Balongan, estimasi dimensi dan posisi pipa, menentukan nilai amplitudo hambur balik pipa dan menganalisis respon hambur balik dari pipa. Pemrosesan data side scan sonar dilakukan menggunakan koreksi geometrik untuk menetapkan posisi yang sebenarnya pada pixel citra yang terdiri dari bottom tracking, slant range correction, layback correction dan koreksi radiometrik dilakukan untuk intensitas hambur balik pada digital number yang ditetapkan pada setiap pixel meliputi Beam Angle Correction (BAC), Automatic Gain Control (AGC), Time Varying Gain (TVG) dan Empirical Gain Normalization (EGN). Lokasi penelitian berada di sekitar Pelabuhan Balongan menggunakan instrumen side scan sonar C-MAX CM2 dengan frekuensi 325 kHz. Pengolahan data menggunakan perangkat lunak SonarWiz 5 dengan melakukan beberapa koreksi yang kemudian data hasil olahan di ekstrak menggunakan perangkat lunak XtfTosegy selanjutnya di ekstrak dengan perangkat lunak Seisee untuk menghasilkan data dengan format *.txt dan hasilnya diolah dengan perangkat lunak Matlab untuk menampilkan grafik yang dapat menunjukan nilai amplitudo dari target yang terdeteksi. Dimensi objek hasil dari pengukuran target yaitu Target pipa 1 memiliki lebar (diameter) 0,9 meter, tinggi 0,64 meter, nilai amplitudo sebesar 23.420 – 32.000 mV dan memiliki nilai hambur balik sebesar -2,71 dB. Target pipa 2 lebar(diameter) 0,9 meter, tinggi 0,35 meter dengan nilai amplitudo 20.104 – 31.100 mV dan memiliki nilai hambur balik sebesar -3,06 dB. Sedangkan target substrat dasar perairan memiliki amplitudo hambur balik 4.480 – 17.660 mV dan nilai hambur balik -11,91 dB. Hasil analisa dapat diartikan bahwa target pipa 1 dan pipa 2 memiliki kekerasan yang lebih dibandingkan dengan dasar laut. Dilihat dari nilai hambur balik dan bentuk secara 2D dipastikan target pipa 1 dan pipa 2 terbuat dari besi dengan nilai impedansi akustik 478,85 x 105 kg/m2s dan koefisien refleksi 0,928.