http://arxiv.org/abs/2211.14245

Space exploration has been on the rise since the 1960s. Along with the other planets such as Mercury, Venus, Saturn, and Jupiter, Mars certainly plays a significant role in the history of space exploration and has the potential to be the first extraterrestrial planet to host human life. In this context, tremendous effort has been put into developing new technologies to photograph, measure, and analyze the red planet. As the amount of data collected from science instruments around and on Mars increased, the need for fast and reliable communication between Earth and space probes has emerged. However, communicating over deep space has always been a big challenge due to the propagation characteristics of radio waves. Nowadays, the collaboration of private companies like SpaceX with space agencies to make Mars colonization a reality, introduces even more challenges, such as providing high data rate, low latency, energy-efficient, reliable, and mobility-resistant communication infrastructures in the Martian environment. Propagation medium and wireless channel characteristics of Mars should be extensively studied to achieve these goals. This survey article presents a comprehensive overview of the Mars missions and channel modeling studies of the near-Earth, interstellar, and near-planet links. Studies featuring three-dimensional (3D) channel modeling simulations on the Martian surface are also reviewed. We have also presented our own computer simulations considering various scenarios based on realistic 3D Martian terrains using the Wireless Insite software. Path loss exponent, power delay profile, and root-mean-square delay spread for these scenarios are calculated and tabularized in this study. Furthermore, future insights on emerging communication technologies for Mars are given.

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E. Koktas and E. Basar
Mon, 28 Nov 22
6/93

Comments: 35 pages, 10 figures

http://arxiv.org/abs/2211.03828

A major threat to satellites is space debris with their low mass and high rotational speed. Accordingly, the short observation time of these objects is a major limitation in space research for appropriate detection and decision. As a result, these objects do not fully illuminated, leading to their incomplete images at any snapshot. In this paper, we propose a method to decrease the number of snapshots in a given observation time and using a limited number of spot beams per snapshot called the encoded aperture. To recover the space debris images, an inverse problem is defined based on compressive sensing methods. Also, we show that for satellite imaging the T V norm is more appropriate. We develop a procedure to recover space debris and satellites using L1 and T V norms. Using simulation results, we compare the results with the well-known SBL and SL0 norm in terms of the number of snapshots, MSE, SNR, and running time. It is shown that our proposed method can successfully recover the space objects images using a fewer number of snapshots.

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M. Roueinfar and M. Kahaei
Wed, 9 Nov 22
1/76

Comments: N/A

http://arxiv.org/abs/2206.02357

This paper describes the use of the Murchison Widefield Array, a low-frequency radio telescope at a radio-quiet Western Australian site, as a radar receiver forming part of a continent-spanning multistatic radar network for the surveillance of space. This paper details the system geometry employed, the orbit-specific radar signal processing, and the orbit determination algorithms necessary to ensure resident space objects are detected, tracked, and propagated. Finally, the paper includes the results processed after a short collection campaign utilising several FM radio transmitters across the country, up to a maximum baseline distance of over 2500 km. The results demonstrate the Murchison Widefield Array is able to provide widefield and persistent coverage of objects in low Earth orbit.

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B. Hennessy, R. Young, S. Tingay, et. al.
Tue, 7 Jun 22
50/70

Comments: N/A

http://arxiv.org/abs/2203.10065

Interstellar communication transmitters, intended to be discovered and decoded to information bits, are expected to transmit signals that contain message symbols quantized in at least one of the degrees of freedom of the transmitted signal. A hypothesis is proposed that signal quantization, in the form of multiplicative values of one or more signal measurements, may be observable during the reception of hypothetical discoverable interstellar communication signals. In previous work, using single and multiple synchronized radio telescopes, candidate hypothetical interstellar communication signals comprising delta-t delta-f opposite circular polarized pulse pairs have been reported and analyzed (ref. arXiv:2105.03727, arXiv:2106.10168, arXiv:2202.12791). In the latter report, an apparent quantization of delta-f at multiples of 58.575 Hz was observed. In the current work, a machine process has been implemented to further examine anomalous delta-f and delta-t quantization, with results reported in this paper. As in some past work, a 26 foot diameter radio telescope with fixed azimuth and elevation pointing is used to enable a Right Ascension filter to measure signals associated with a celestial direction of interest, relative to other directions, over a 6.3 hour range of Right Ascension. The 5.25 plus or minus 0.15 hour Right Ascension, -7.6 degrees plus or minus 1 degree Declination celestial direction presents repetition and quantization anomalies, during an experiment lasting 157 days, with the first 143 days overlapping the previous experiment.

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W. Jr
Mon, 21 Mar 22
7/60

Comments: 9 pages, 11 figures

http://arxiv.org/abs/2202.12791

Discoverable interstellar communication signals are expected to exhibit al least one signal characteristic clearly distinct from random noise. A hypothesis is proposed that radio telescope received signals may contain transmitted delta-t delta-f opposite circular polarized pulse pairs, conveying a combination of information content and discovery methods, including symbol repetition. Hypothetical signals are experimentally measured using a 26 foot diameter radio telescope, a chosen matched filter receiver, and machine post processing system. Measurements are expected to present likelihoods explained by an Additive White Gaussian Noise model, augmented to reduce radio frequency interference. In addition, measurements are expected to present no significant differences across a population of Right Ascension ranges, during long duration experiments. The hypothesis and experimental methods described in this paper are based on multiple radio telescope delta-t delta-f polarized pulse pair experiments previously reported. (ref. arXiv:2105.03727, arXiv:2106.10168). In the current work, a Right Ascension filter spans twenty-one 0.3 hour Right Ascension bins over a 0 to 6.3 hr range, during a 143 day experiment. Apparent symbol repetition is measured and analyzed. The 5.25 plus or minus 0.15 hr Right Ascension, -7.6 degree plus or minus 1 degree Declination celestial direction has been associated with anomalous observations in previous work, and continues to present anomalies, having unknown cause.

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W. Jr
Mon, 28 Feb 22
11/38

Comments: 12 pages, 12 figures

http://arxiv.org/abs/2111.01184

We consider imaging of fast moving small objects in space, such as low earth orbit satellites, which are also rotating around a fixed axis. The imaging system consists of ground based, asynchronous sources of radiation and several passive receivers above the dense atmosphere. We use the cross-correlation of the received signals to reduce distortions from ambient medium fluctuations. Imaging with correlations also has the advantage of not requiring any knowledge about the probing pulse and depends weakly on the emitter positions. We account for the target’s orbital velocity by introducing the necessary Doppler compensation. To image a fast rotating object we also need to compensate for the rotation. We show that the rotation parameters can be extracted directly from the auto-correlation of the data before the formation of the image. We then investigate and analyze an imaging method that relies on backpropagating the cross-correlation data structure to two points rather than one, thus forming an interference matrix. The proposed imaging method consists of estimating the reflectivity as the top eigenvector of the migrated cross-correlation data interference matrix. We call this the rank-1 image and show that it provides superior image resolution compared to the usual single-point migration scheme for fast moving and rotating objects. Moreover, we observe a significant improvement in resolution due to the rotation leading to a diffraction limited resolution. We carry out a theoretical analysis that illustrates the role of the two point migration method as well as that of the inverse aperture and rotation in improving resolution. Extensive numerical simulations support the theoretical results.

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M. Leibovich, G. Papanicolaou and C. Tsogka
Wed, 3 Nov 21
3/106

Comments: arXiv admin note: text overlap with arXiv:2003.00131

http://arxiv.org/abs/2106.11020

We report the first Vivaldi arrays monolithically fabricated exclusively using commercial, low-cost, 3D metal printing (direct metal laser sintering). Furthermore, we developed one of the first dual-polarized Vivaldi arrays on a triangular lattice, and compare it to a square lattice array. The triangular lattice is attractive because it has a 15.5% larger cell size compared to the square lattice and can be more naturally truncated into a wide range of aperture shapes such as a rectangle, hexagon, or triangle. Both arrays operate at 3-20 GHz and scan angles out to 60 degree from normal. The fabrication process is significantly simplified compared to previously published Vivaldi arrays since the antenna is ready for use directly after the standard printing process is complete. This rapid manufacturing is further expedited by printing the ‘Sub-Miniature Push-on, Micro’ (SMPM) connectors directly onto the radiating elements, which simplifies assembly and reduces cost compared to utilizing discrete RF connectors. The arrays have a modular design that allow for combining multiple sub-arrays together for arbitrarily increasing the aperture size. Simulations and measurement show that our arrays have similar performance as previously published Vivaldi arrays, but with simpler fabrication.

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C. Pfeiffer, J. Massman and T. Steffen
Tue, 22 Jun 21
43/71

Comments: IEEE Transactions on Antennas and Propagation

http://arxiv.org/abs/2106.10168

The discovery of interstellar communication signals is complicated by the presence of radio interference. Consequently, interstellar communication signals are hypothesized to have properties that favor discovery in high levels of local planetary radio interference. A hypothesized type of interstellar signal, delta-t delta-f polarized pulse pairs, has properties that are similar to infrequent elements of random noise, while dissimilar from many types of known radio interference. Discovery of delta-t delta-f polarized pulse pairs is aided by the use of interference-filtered receiver systems that are designed to indicate anomalous presence of delta-t delta-f polarized pulse pairs, when pointing a radio telescope to celestial coordinates of a hypothetical transmitter. Observations reported in previous work (ref. arXiv:2105.03727) indicate an anomalous celestial pointing direction having coordinates 5.25 +- 0.15 hours Right Ascension and -7.6 +- 1 degrees Declination. Augmented interference reduction mechanisms used in the current work are described, together with reports of follow-up radio telescope beam transit measurements during 40 days. Conclusions and further work are proposed.

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W. Jr
Mon, 21 Jun 21
28/54

Comments: 10 pages, 13 figures

http://arxiv.org/abs/2105.03727

A system of synchronized radio telescopes is utilized to search for hypothetical wide bandwidth interstellar communication signals. Transmitted signals are hypothesized to have characteristics that enable high channel capacity and minimally low energy per information bit, while containing energy-efficient signal elements that are readily discoverable, distinct from random noise. A hypothesized transmitter signal is described. Signal reception and discovery processes are detailed. Observations using individual and multiple synchronized radio telescopes, during 2017 – 2021, are described. Conclusions and further work are suggested.

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W. Jr
Tue, 11 May 21
49/93

Comments: 22 pages, 22 figures

http://arxiv.org/abs/2012.05133

End-to-end mission performance simulators (E2ES) are suitable tools to accelerate satellite mission development from concet to deployment. One core element of these E2ES is the generation of synthetic scenes that are observed by the various instruments of an Earth Observation mission. The generation of these scenes rely on Radiative Transfer Models (RTM) for the simulation of light interaction with the Earth surface and atmosphere. However, the execution of advanced RTMs is impractical due to their large computation burden. Classical interpolation and statistical emulation methods of pre-computed Look-Up Tables (LUT) are therefore common practice to generate synthetic scenes in a reasonable time. This work evaluates the accuracy and computation cost of interpolation and emulation methods to sample the input LUT variable space. The results on MONDTRAN-based top-of-atmosphere radiance data show that Gaussian Process emulators produced more accurate output spectra than linear interpolation at a fraction of its time. It is concluded that emulation can function as a fast and more accurate alternative to interpolation for LUT parameter space sampling.

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J. Vicent, J. Verrelst, J. Rivera-Caicedo, et. al.
Thu, 10 Dec 20
64/87

Comments: Preprint, paper published in IGARSS 2018 – 2018 IEEE International Geoscience and Remote Sensing Symposium, Valencia, 2018, pp. 1699-1702

http://arxiv.org/abs/2003.03947

This paper presents a novel algorithm to incorporate orbital parameters into radar ambiguity function expressions by extending the standard ambiguity function to match Keplerian two-body orbits. A coherent orbital matched-filter will maximise a radar’s sensitivity to objects in orbit, as well as provide rapid initial orbit determination from a single detection. This paper then shows how uncued detection searches can be practically achieved by incorporating radar parameters into the orbital search-space, especially for circular orbits. Simulated results are compared to results obtained from ephemeris data, showing that the orbital path determined by the proposed method, and the associated radar parameters that would be observed, match those derived from the ephemeris data.

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B. Hennessy, M. Rutten, S. Tingay, et. al.
Tue, 10 Mar 20
2/63

Comments: N/A

http://arxiv.org/abs/1910.04435

In this paper we build upon recent work in the radio astronomy community to experimentally demonstrate the viability of passive radar for Space Situational Awareness. Furthermore, we show that the six state parameters of objects in orbit may be measured and used to perform orbit characterisation/estimation.

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J. Palmer, B. Hennessy, M. Rutten, et. al.
Fri, 11 Oct 19
45/76

Comments: Published in: 2017 IEEE Radar Conference (RadarConf) URL: this http URL&arnumber=7944483&isnumber=7944108

http://arxiv.org/abs/1812.06972

This Resolution Team 3 (RT-3) report contains the results of the investigation of key aspects of the proposed Sample Clock Frequency Offset (SCFO) scheme for the Mid SKA1 telescope. This is a scheme, first proposed by one author (Carlson) at a meeting at the SKAO 25-Jan-2013, to digitize the analog signal at each antenna at a slightly different sample rate and transmit the data to the CSP Mid.CBF for subsequent digital re-sampling to a common sample clock frequency before channelization, correlation, and beamforming. The primary purpose for doing this is to cause de-correlation of sample clock-related self-interference to be able to improve correlated and beamformed signal quality. This report includes an investigation of the efficacy of the method, investigation of its implementation by SADT, DISH, and CSP, presentation of further supporting modeling results augmenting the original modeling work, a note on expansion to SKA-2, as well as possible draw-backs and concerns. Finally, there are potential additional benefits in signal quality in implementing the SCFO scheme, in particular de-correlation of aliased RFI (particularly for Nyquist Zone-2 digitized signals) as well as relaxation of signal-chain anti-aliasing filters transition band roll-off and reject band attenuation prior to digitization in the antenna.

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B. Carlson, P. Boven and K. Caputa
Wed, 19 Dec 18
34/84

Comments: 44 pages, 20+ figures

http://arxiv.org/abs/1812.05498

The proliferation of relatively affordable off-the-shelf drones offers great opportunities for wildlife monitoring and conservation. Similarly the recent reduction in cost of thermal infrared cameras also offers new promise in this field, as they have the advantage over conventional RGB cameras of being able to distinguish animals based on their body heat and being able to detect animals at night. However, the use of drone-mounted thermal infrared cameras comes with several technical challenges. In this paper we address some of these issues, namely thermal contrast problems due to heat from the ground, absorption and emission of thermal infrared radiation by the atmosphere, obscuration by vegetation, and optimizing the flying height of drones for a best balance between covering a large area and being able to accurately image and identify animals of interest. We demonstrate the application of these methods with a case study using field data, and make the first ever detection of the critically endangered riverine rabbit (Bunolagus monticularis) in thermal infrared data. We provide a web-tool so that the community can easily apply these techniques to other studies (this http URL).

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C. Burke, M. Rashman, S. Wich, et. al.
Fri, 14 Dec 18
58/58

Comments: Accepted for publication in International Journal of Remote Sensing: Drones. 30 pages, 13 figures

http://arxiv.org/abs/1809.10086

Space Vehicle (SV) life span depends on its station keeping capability. Station keeping is the ability of the vehicle to maintain position and orientation. Due to external perturbations, the trajectory of the SV derives from the ideal orbit. Actual positioning systems for satellites are mainly based on ground equipment, which means heavy infrastructures. Autonomous positioning and navigation systems using Global Navigation Satellite Systems (GNSS) can then represent a great reduction in platform design and operating costs. Studies have been carried out and the first operational systems, based on GPS receivers, become available. But better availability of service could be obtained considering a receiver able to process GPS and Galileo signals. Indeed Galileo system will be compatible with the current and the modernized GPS system in terms of signals representation and navigation data. The greater availability obtained with such a receiver would allow significant increase of the number of point solutions and performance enhancement. For a mid-term perspective Thales Alenia Space finances a PhD to develop the concept of a reconfigurable receiver able to deal with both the GPS system and the future Galileo system. In this context, the aim of this paper is to assess the performances of a receiver designed for Geosynchronous Earth Orbit (GEO) applications. It is shown that high improvements are obtained with a receiver designed to track both GPS and Galileo satellites. The performance assessments have been used to define the specifications of the future satellite GNSS receiver.

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A. Dion, V. Calmettes, M. Bousquet, et. al.
Thu, 27 Sep 18
52/68

Comments: N/A

http://arxiv.org/abs/1809.04533

Radio Searches for Extra Terrestrial Intelligence aim at detecting artificial transmissions from extra terrestrial communicative civilizations. The lack of prior knowledge concerning these potential transmissions increase the search parameter space. Ground-based single dish radio telescopes offer high sensitivity, but standard data products are limited to power spectral density estimates. To overcome important classical energy detector limitations, two detection strategies based on asynchronous ON and OFF astronomical target observations are proposed. Statistical models are described to enable threshold selection and detection performance assessment.

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G. Hellbourg
Thu, 13 Sep 18
49/68

Comments: N/A

http://arxiv.org/abs/1809.03547

The radio Search for Extra Terrestrial Intelligence (SETI) aims at identifying intelligent and communicative civilizations in the Universe through the detection of engineered transmissions. In the absence of prior knowledge concerning the expected signal, SETI detection pipelines necessitate high sensitivity, versatility, and limited computational complexity to maximize the search parameter space and minimize the probability of misses. This paper addresses the SETI detection problem as a binary hypothesis testing problem, and compares four detection schemes exploiting artificial features of the data collected by a single receiver radio telescope. After a theoretical comparison, those detectors are applied to real data collected with the Green Bank Telescope in West Virginia (USA).

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G. Hellbourg and A. Xu
Wed, 12 Sep 18
42/73

Comments: N/A

http://arxiv.org/abs/1809.03620

Active Radio Frequency Interference (RFI) mitigation becomes a necessity for radio astronomy. The solution commonly applied by the community consists in monitoring the statistics of the received signal, and flag out the detected corrupted data. Subspace projection with array radio telescopes has been suggested as an alternative to data excision to avoid important losses of data and overcome its inherent ineffectiveness with continuous interference. Spatial filtering relies on the estimation of the RFI spatial contribution, and the projection of the subspace spanned by the RFI out of the observed data vector space. To perform well, the dimensionality of the RFI subspace is constrained. RFI subspace estimation techniques assume the source of RFI to be spatially stationary over the sample covariance matrix evaluation. When the relative movement between the telescope and the interferer becomes significant, the RFI subspace gets smeared over the whole data vector space. The subspace projection can then no longer be applied without affecting the source of interest recovery. This paper addresses the effect of RFI subspace smearing on the subspace projection approach, and suggests an alternative technique based on a covariance matrix subtraction, improving the performance of spatial filtering in the case of high subspace smearing.

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G. Hellbourg
Wed, 12 Sep 18
67/73

Comments: N/A

http://arxiv.org/abs/1806.01321

A dedicated codec for compression of gravitational waves sound with high quality recovery is proposed. The performance is tested on the available set of gravitational sound signals that has been theoretically generated at the Massachusetts Institute of Technology (MIT). The approach is based on a model for data reduction rendering high quality approximation of the signals. The reduction of dimensionality is achieved by selecting elementary components from a redundant set called a dictionary. Comparisons with the compression standard MP3 demonstrate the merit of the dedicated technique for compressing this type of sound.

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L. Rebollo-Neira
Wed, 6 Jun 18
51/68

Comments: All the results in this paper can be reproduced using the MATLAB software which has been made available on this http URL

http://arxiv.org/abs/1711.07421

This article analyzes the data for the five gravitational wave (GW) events detected in Hanford(H1), Livingston(L1) and Virgo(V1) detectors by the LIGO collaboration. It is shown that GW170814, GW170817, GW151226 and GW170104 are very weak signals whose amplitude does not rise significantly during the GW event, and they are indistinguishable from non-stationary detector noise. LIGO software implements cross-correlation funcion(CCF) of H1/L1 signals with the template reference signal, in frequency domain, in a matched filter, using 32 second windows. It is shown that this matched filter misfires with high SNR/CCF peaks, even for very low-amplitude, short bursts of sine wave signals and additive white gaussian noise(AWGN), all the time. It is shown that this erratic behaviour of the matched filter, is due to the error in signal processing operations, such as lack of cyclic prefix necessary to account for circular convolution. It is also shown that normalized CCF method implemented in time domain using short windows, does not have false CCF peaks for sine wave and noise bursts. It is shown that the normalized CCF for GW151226 and GW170104, when correlating H1/L1 and template, is indistinguishable from correlating detector noise and the template. It is also shown that the normalized CCF for GW151226 and GW170104, when correlating H1/L1 and template, is indistinguishable from correlating H1/L1 and bogus chirp templates which are frequency modulated(FM) waveforms which differ significantly from ideal templates. Similar results are shown with LIGO matched filter, which misfires with high Signal to Noise Ratio(SNR) for bogus chirp templates.

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A. Raman and B. Antony
Tue, 21 Nov 17
79/79

Comments: Please post to EESS.SP