Solar wind-Venus interaction affecting ionospheric electron density profile

The equilibrium electron density profile has been computed and compared with measured profiles by Venera 9 and Mariner 5 and 10. The computed electron density profile is seen to show discrepancies with measured data. The contribution of solar wind interaction induced convection to equilibrium electron density profile has been estimated. It is found that the convective processes are less important at lower altitudes, whereas at higher altitudes its contribution becomes dominant. The night side Venus ionosphere is formed due to the transport of O⁺ and impact ionization of neutral gases by suprathermal electrons. The discrepancies in theoretical and measured electron density profiles provide clear indication of additional energy source of solar wind origin.     

Seismogenic ionospheric anomalies associated with the strong Indonesian earthquake occurred on 11 April 2012 (M = 8.5)

Ionospheric perturbations in possible association with a major earthquake (EQ) (M?=?8.5) which occurred in India-Oceania region are investigated by monitoring subionospheric propagation of VLF signals transmitted from the NWC transmitter (F?=?19.8?kHz), Australia to a receiving station at Varanasi (geographic lat. 25.3°N, long 82.99°E), India. The EQ occurred on 11 April 2012 at 08:38:35?h UT (magnitude?≈?8.5, depth?=?10?km, and lat.?=?2.3°N, long.?=?93.0°E). A significant increase of few days before the EQ has been observed by using the VLF nighttime amplitude fluctuation method (fixed frequency transmitter signal). The analysis of total electron contents (TEC) derived from the global positioning system (GPS) at three different stations namely, Hyderabad (latitude 17.38°N, longitude 78.48°E), Singapore (latitude 1.37°N, longitude 103.84°E) and Port Blair (latitude 11.62°N, longitude 92.72°E) due to this EQ has also been presented. Significant perturbation in TEC data (enhancements and depletion) is noted before and after the main shock of the EQ. The possible mechanisms behind these perturbations due to EQ have also been discussed.     

Anomalous TEC variations associated with the strong Pakistan-Iran border region earthquake of 16 April 2013 at a low latitude station Agra,India

Employing a dual frequency GPS-receiver, ionospheric total electron (TEC) measurements have been in progress at Agra station in India (Geograph. lat. 27.2°N, long. 78°E) since 1 April 2006. In this paper, the TEC data have been analyzed for a period of one month from 1 April-1 May 2013 to examine the effect of multiple earthquakes, some of which occurred on the same day of 16 April 2013, and others occurred in the same month of April, 2013 in India and neighboring countries. We process the data using quartile and epoch analysis based statistical techniques and show that out of all the earthquakes, the one of the largest magnitude (M = 7.8) that occurred on Pakistan-Iran border caused anomalous enhancements and depletions in TEC 1–9 days before the occurrence of main sock. The E × B drift mechanism is suggested for the anomalies to occur in which the seismogenic electric field E is generated in a process suggested by Pulinets (2004).     

Extended Pile Driving Model to Predict the Penetration of the Insight/HP<Superscript>3</Superscript> Mole into the Martian Soil

The NASA InSight mission will provide an opportunity for soil investigations using the penetration data of the heat flow probe built by the German Aerospace Center DLR. The Heat flow and Physical Properties Probe (HP³) will penetrate 3 to 5 meter into the Martian subsurface to investigate the planetary heat flow. The measurement of the penetration rate during the insertion of the HP³ will be used to determine the physical properties of the soil at the landing site. For this purpose, numerical simulations of the penetration process were performed to get a better understanding of the soil properties influencing the penetration performance of HP³. A pile driving model has been developed considering all masses of the hammering mechanism of HP³. By cumulative application of individual stroke cycles it is now able to describe the penetration of the Mole into the Martian soil as a function of time, assuming that the soil parameters of the material through which it penetrates are known. We are using calibrated materials similar to those expected to be encountered by the InSight/HP³ Mole when it will be operated on the surface of Mars after the landing of the InSight spacecraft. We consider various possible scenarios, among them a more or less homogeneous material down to a depth of 3–5 m as well as a layered ground, consisting of layers with different soil parameters. Finally we describe some experimental tests performed with the latest prototype of the InSight Mole at DLR Bremen and compare the measured penetration performance in sand with our modeling results. Furthermore, results from a 3D DEM simulation are presented to get a better understanding of the soil response.     

Nonlinear adaptive spacecraft attitude control using solar radiation pressure

Spacecraft and interplanetary probes orbiting at high altitudes experience forces due to solar radiation pressure, which can be used for maneuvering. The question of large angle pitch attitude maneuvers of satellites using solar radiation torque is considered. For pitch axis maneuver, two highly reflective control surfaces are used to generate radiation moment. The solar radiation moment is a complex nonlinear function of the attitude and parameters of the satellite, the orbital parameters, and the deflection angles of the reflective control surfaces. It is assumed that the parameters of the satellite model are unknown. Based on a backstepping design technique, a nonlinear adaptive control law is derived for the control of the pitch angle. In the closed-loop system, the pitch angle asymptotically tracks prescribed reference trajectories. Simulation results are presented to show that the adaptive control system accomplishes attitude control of the satellite in spite of the parameter uncertainties in the system.     

Tracking for maneuvering target trajectories via the 3D circular filter

A circular prediction algorithm is proposed, which integrates the measured data into the filter and constrains the prediction to lie on a smooth curve modeled by an arc of a circle. The circular prediction is entirely defined in relation to three measurements in three-dimensional space. It is therefore not necessary to calculate the center and the radius of the circle. To obtain the statistics of the circular prediction, the unscented transformation has been utilized. The proposed hybrid filter combines the circular prediction and a constant velocity prediction by utilizing the covariance intersection (CI). This combined prediction can be updated with the subsequent measurement using a linear estimator. The proposed technique is compared with standard filters and the interacting multiple model (IMM) approach on a benchmark trajectory which includes coordinated turns and straight line maneuvers.     

Benefits and challenges of voluntary contribution to GEOSS

The vision of the Global Earth Observation System of Systems (GEOSS) is the achievement of societal benefits through voluntary contribution and sharing of data, metadata and products at no or minimum cost. Such undertakings, where contribution provides positive externalities, benefiting contributors and non-contributors alike, are often described as ‘social dilemmas’, usually resulting in small levels of voluntary contribution. We investigate the benefits and challenges of voluntary contribution to GEOSS, surveying economic and game theoretic literature and examining how the concepts of social dilemmas apply to the provision of GEOSS. We conduct an exploratory survey among individuals involved in the Group on Earth Observation (GEO) to understand their perception of voluntarily contribution. Even though contribution to GEOSS was perceived as rather low, e.g. because of a perceived lack of funds, commitment or organization, survey respondents also perceived many (exclusive) benefits of contribution, e.g. networking, visibility for their work or collaborating with motivated individuals. To increase participation, respondents suggested increasing financial support and raising awareness of GEOSS. We conclude that communicating the efficacy of individuals' contributions, the personal benefits of contribution and strengthening of group identity and knowledge about fellow participants' work can constitute incentives for future voluntary contribution. This could be facilitated by an externally established institution providing a framework for cooperation, or by institutions, agreements or frameworks agreed upon by contributors themselves.     

A relative clutter metric

Clutter plays a very important role in the area of machine and human-in-the-loop target acquisition. A great deal of interest has recently been shown in assessing several different definitions of clutter. In spite of so many definitions available, no single clutter definition has been agreed on by the infrared community as being the best. We develop a new clutter metric, called relative clutter, which is based on factor analysis which is extensively used for statistical analysis. This relative clutter combines many definitions of clutter. Different methods for calculating the relative clutter based on the magnitude of the eigenvalues obtained from the correlation matrix are suggested. The relative clutter of many images is analyzed     

Novel data association schemes for the probability hypothesis density filter

The probability hypothesis density (PHD) filter is a practical alternative to the optimal Bayesian multi-target Alter based on finite set statistics. It propagates the PHD function, a first-order moment of the full multi-target posterior density. The peaks of the PHD function give estimates of target states. However, the PHD filter keeps no record of target identities and hence does not produce track-valued estimates of individual targets. We propose two different schemes according to which PHD filter can provide track-valued estimates of individual targets. Both schemes use the probabilistic data-association functionality albeit in different ways. In the first scheme, the outputs of the PHD filter are partitioned into tracks by performing track-to-estimate association. The second scheme uses the PHD filter as a clutter filter to eliminate some of the clutter from the measurement set before it is subjected to existing data association techniques. In both schemes, the PHD filter effectively reduces the size of the data that would be subject to data association. We consider the use of multiple hypothesis tracking (MHT) for the purpose of data association. The performance of the proposed schemes are discussed and compared with that of MHT.