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In this article, we designed a wideband square spiral antenna with an impedance matching part that operated between 1500 - 5500 MHz (covering L, S, and C bands) for airborne uses such as Aeronautical Mobile Satellite Service, radar altimeters, Microwave Landing System, and airborne weather radars. The impedance matching part was a designed wideband balun. We obtained simulation results for scattering parameters, radiation patterns, antenna and system input impedances and gain values. The results confirmed that the antenna showed good matching and radiation characteristics within the mentioned frequency range. [ABSTRACT FROM AUTHOR]

Mobile LiDAR Systems (MLSs) have recently been recognized as an effective way to extract road markings. Although existing studies have achieved good accuracy (about 90%) in road marking extraction, the majority of them are based on image processing methods; only a few researchers directly use laser points, especially for the recognition and assessment of road markings. This study introduces a three-step automated method for the extraction, recognition, and maintenance of road markings based on the intensity information from the MLS data: (1) an automated mechanism to filter the ground surface in laser data, (2) an adaptive block and multi-threshold method to detect road markings, (3) an automated method to achieve the classification, recognition, and assessment of road markings. Qualitative and quantitative analyses based on experimental datasets with eight types of road markings were used to evaluate the feasibility and robustness of the proposed method. Experimental results show that the average values of completeness (CPT), correctness (CRT), and F-measure of the road marking detection results are 94.35%, 98.35%, and 95.7% and the average values of CPT, CRT, and quality (QUA) of recognition results are 99.0%, 93.2%, and 92.3%, respectively, indicating that the proposed method is feasible and effective. The detection and recognition results were used to reconstruct, improve, and update the road features database; provide guidelines for road applications and maximum assistance for road maintenance; and deliver a valuable solution for maintenance and management of constructed facilities. [ABSTRACT FROM AUTHOR]

The positional inaccuracies associated with the GPS/INS measurements make the terminal phase of the normal GPS/INS landing system imprecise. To solve this problem, an adaptive fuzzy data fusion algorithm is developed to obtain more accurate state estimates while the vehicle approaches the landing surface. This algorithm takes the translational displacements in x and y from the mounted Optical Flow (OF) sensor and fuses them with the INS attitude measurements and the altimeter measurements. This low cost adaptive algorithm can be used for vertical landings in areas where GPS outages might happen or in GPS denied areas. The adaptation is governed by imposing appropriate assumptions under which the filter measurement noise matrix R is predicted. The R matrix is continuously adjusted through a fuzzy inference system (FIS) based on the Kalman innovative sequence and the applied covariance-matching technique. This adaptive fuzzy Kalman fusion algorithm (AFKF) is used to estimate the vehicle’s states while landing is being commanded. AFKF results are compared with these obtained using a classical Kalman estimation technique. The AFKF algorithm shows better states estimates than its conventional counterpart does. Compared to prior landing systems, the proposed low cost AFKF has achieved a precision landing with less than 10 cm maximum estimated position error. Real precision landing flights were conducted to demonstrate the validity of the proposed intelligent estimation method. [ABSTRACT FROM AUTHOR]

Ozone and temperature profiles of the satellite microwave limb sounder Aura/MLS are used for the derivation of the middle atmospheric response to the geomagnetic superstorm of 9 November 2004. We find a destruction of the tertiary ozone layer at 0.022 hPa (77 km) in the northern winter hemisphere lasting for about one week. This effect is surely due to the solar proton event (SPE) of November 2004. At the same time, the zonal mean temperature is enhanced by 5–10 K in the northern polar mesosphere. On the other hand, the zonal mean temperature is decreased by 5–10 K in the northern polar stratosphere. We do not think that the strong temperature perturbations are directly related to the SPE. It seems that the polar vortex was moved by the geomagnetic storm, and this vortex movement caused the strong temperature variations in the zonal mean. However, internal variability of temperature in the polar middle atmosphere in winter without any significant link to the geomagnetic storm cannot be excluded. [ABSTRACT FROM AUTHOR]

The goal of this work is to inter-compare a number of global land surface emissivity products over various land-cover conditions to assess their consistency. Ultimately, the discrepancies between the studied emissivity products will help interpreting the divergences among numerical weather prediction models in which land emissivity is a key surface boundary parameter. The intercompared retrieved land emissivity products were generated over five-year period (2003-2007) using observations from the Advanced Microwave Scanning Radiometer - Earth Observing System (AMSR-E), Special Sensor Microwave Imager (SSM/I), The Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI) and Windsat. First, all products were reprocessed in the same projection and spatial resolution as they were generated from sensors with various configurations. Then, the mean value and standard deviations of monthly emissivity values were calculated for each product to assess the spatial distribution of the consistencies/inconsistencies among the products across the globe. The emissivity values from four products were also compared to soil moisture estimates and satellite-based vegetation index to assess their sensitivities to the changes in land surface conditions. Results show that systematic differences among products exist and variation of emissivities at each product has similar frequency dependency at any land cover type. Monthly means of emissivity values from AMSR-E in the vertical and horizontal polarizations seem to be systematically lower across various land cover condition which may be attributed to the 1.30 a.m./p.m. overpass time of the sensor and possibly a residual skin temperature effect in the product. The standard deviation of the analysed products was the lowest (less than 0.01) in rain forest regions for all products and the highest in northern latitudes, above 0.04 for AMSR-E and SSM/I and around 0.03 for WindSat. Despite differences in absolute emissivity estimates, all products were similarly sensitive to changes in soil moisture and vegetation. The correlation between the emissivity polarization differences and NDVI values showed similar spatial distribution across the products with values close to the unit except over densely vegetated and desert areas. [ABSTRACT FROM AUTHOR]

Sulphur dioxide (SO2) is an important atmospheric constituent, particularly in the aftermath of volcanic eruptions. These events can inject large amounts of SO2 into the lower stratosphere, where it is oxidised to form sulphate aerosols; these in turn have a significant effect on the climate. The MLS instrument on the Aura satellite has observed the SO2 mixing ratio in the upper troposphere and lower stratosphere from August 2004 to these present, during which time a number of volcanic eruptions have significantly affected those regions of the atmosphere. We describe the MLS SO2 data and how various volcanic events appear in the data. As the MLS SO2 data are currently not validated we take some initial steps towards their validation. First we establish the level of internal consistency between the three spectral regions in which MLS is sensitive to SO2. We compare SO2 column values calculated from MLS data to total column values reported by the OMI instrument. The agreement is good in cases where the SO2 is clearly at altitudes above 147 hPa. [ABSTRACT FROM AUTHOR]

Abstract: Robotic planetary surface exploration missions are becoming much more ambitious in their science goals as they attempt to answer the bigger questions relating to the possibility of life elsewhere in our solar system. Answering these questions will require scientifically rich landing sites. Such sites are unlikely to be located in relatively flat regions that are free from hazards, therefore there is a growing need for next generation entry descent and landing systems to possess highly sophisticated navigation capabilities coupled with active hazard avoidance that can enable a pin-point landing. As a first step towards achieving these goals, a multi-source, multi-rate data fusion algorithm is presented that combines single camera recursive feature-based structure from motion (SfM) estimates with measurements from an inertial measurement unit in order to overcome the scale ambiguity problem by directly estimating the unknown scale factor. This paper focuses on accurate estimation of absolute motion parameters, as well as the estimation of sparse landing site structure to provide a starting point for hazard detection. We assume no prior knowledge of the landing site terrain structure or of the landing craft motion in order to fully assess the capabilities of the proposed algorithm to allow a pin-point landing on distant solar system bodies where accurate knowledge of the desired landing site may be limited. We present results using representative synthetic images of deliberately challenging landing scenarios, which demonstrates that the proposed method has great potential. [Copyright &y& Elsevier]

From 19 November to 19 December 2010 the fourth and final ECOMA rocket campaign was conducted at Andøya Rocket Range (69° N, 16° E) in northern Norway. We present and discuss measurement results obtained during the last rocket launch labelled ECOMA09 when simultaneous and true common volume in situ measurements of temperature and turbulence supported by ground-based lidar observations reveal two Mesospheric Inversion Layers (MIL) at heights between 71 and 73 km and between 86 and 89 km. Strong turbulence was measured in the region of the upper inversion layer, with the turbulent energy dissipation rates maximising at 2Wkg-1. This upper MIL was observed by the ALOMAR Weber Na lidar over the period of several hours. The spatial extension of this MIL as observed by the MLS instrument onboard AURA satellite was found to be more than two thousand kilometres. Our analysis suggests that both observed MILs could possibly have been produced by neutral air turbulence. [ABSTRACT FROM AUTHOR]

Abstract: This study provides a theoretical/physical framework to quantify the vegetation scattering effects on radiometric microwave measurements of soil moisture. The model development and analysis is presented to assess the limitations of the existing τ − ω (tau-omega) model with respect to vegetated landscapes and thus to extend the usefulness of the τ − ω model to a wider range of vegetation conditions. An explicit expression is driven for an effective albedo of vegetated terrain from the zero- and multiple-order radiative transfer solutions. The formulation establishes a direct physical link between the effective vegetation parameterization and the theoretical description of absorption and scattering within the canopy. Evaluation of the derived albedo for corn canopies (stem-dominated vegetation) with data taken during the Huntsville 1998 field experiment (Hsv98) are shown and discussed. The simulation results are in good agreement with the data and show that the effective albedo values are significantly smaller than the single-scattering albedo values and increase monotonically as soil moisture increases. The model is also used to simulate effective albedo from a soybean canopy (leaf dominated vegetation) at L-band. Both results illustrate that the fitted albedo values, which are found in the literature, represent effective albedo values rather than the single-scattering albedo values. [Copyright &y& Elsevier]

A MLS-based lattice spring model is presented for numerical modeling of elasticity of materials. In the model, shear springs between particles are introduced in addition to normal springs. However, the unknowns contain only particle displacements but no particle rotations. The novelty of the model lies in that the deformations of shear springs are computed by using the local strain obtained by the moving least squares (MLS) approximation rather than using the particle displacements directly. By doing so, the proposed lattice spring model can represent the diversity of Poisson's ratio without violating the requirement of rotational invariance. Relationships between micro spring parameters and macro material constants are derived from the Cauchy-born rules and the hyperelastic theory. Numerical examples show that the proposed model is able to reproduce elastic solutions obtained by finite element methods for problems without fractures. Therefore, it is capable of simulating solid materials which are initially continuous, but eventually fracture when critical stress and/or displacement levels are reached. A demonstrating example is presented. [ABSTRACT FROM AUTHOR]

This paper presents an experimental study of air-to-ground channels over sea surface at the C-band (5.7 GHz) with low airborne altitudes (0.37–1.83 km) through wideband channel measurements. In this paper, the multipath statistics and the propagation loss at different airborne altitudes are estimated and analyzed. It is observed that about 95% (86%) of the measured channel responses can be represented by the 3-ray (2-ray) multipath model. As the airborne altitude decreases, there is a higher probability for the appearance of multipath components. Moreover, it is found that the evaporation duct and elevated duct over the sea surface are the two important factors that can significantly affect the over-water air-to-ground communication link. These ducts can also decrease the rate of radio-wave attenuation, i.e., a decrease in path-loss exponent n in the log-distance path-loss models. [ABSTRACT FROM PUBLISHER]

The GPS landing system (GLS) is a reality today, and will undoubtedly become the workhorse system in the future. GPS aircraft navigation is currently utilized for aircraft en-route, terminal, and initial-approach navigation. It is expected that in 2009, a Category I GPS landing system will start its initial phase of a worldwide deployment. The ARL-1900 antenna was designed specifically to satisfy the stringent requirements for the Category I, II, and III GPS landing system reference-receiver stations. A difficult problem for a Category I, II, and III GPS landing systems is the mitigation of ground-reflected multipath effects. The antenna must provide coverage of the upper hemisphere while suppressing ground-reflected multipath. In addition, the antenna must operate at the L1, L2, and L5 GPS frequencies, have right-hand circular polarization, and ideally have constant carrier and code (group) delay throughout the coverage region. Over a period of 15 years, BAE Systems has developed the ARL-1900 antenna, a unique antenna with near-ideal performance that satisfies the stringent requirements for a Category I, II, and III GPS landing systems. This paper reviews the requirements for a GPS landing system reference antenna, presents the design principles for the ARL-1900 antenna, describes its implementation, and presents performance data. [ABSTRACT FROM AUTHOR]

Vertical guidance for an instrument approach to landing during conditions of reduced visibility is a crucial element with respect to safety of flight. It is noteworthy that this vertical component-to be most useful and safe-must desirably provide the pilot with no more than several feet of uncertainty. Unfortunately, with GPS the vertical portion of the position information supplied the pilot by GPS signals is the least precise because of geometries involved. Augmentation for enhancement of accuracy is quite important and the assertion is that it is necessary for totally safe vertical guidance. Evidence from approximately 60 years of experience with electronic landing systems serving the public is that there has been no aircraft accident due to a defective vertical guidance signal. Visibilities as low as 600 feet horizontally can exist at certain airports and landings can still be accomplished. These landings, while not common, are being accomplished flawlessly by contemporary aircraft and equipment. Many aspects of the contemporary UHF glide slope have been studied during its half-century of use. This paper reports on advances, some of them quite recent, that make it realistic to claim that a glide slope can be sited for Category I operation at any runway that meets the physical requirements for this type of operation. For the UHF glide slope, siting imperfections are accommodated by using one of five available types of contemporary glide slope systems or derivatives thereof. This paper reviews how accommodations are achieved in practical cases. Results from earlier tests are identified which show hybridizing of UHF glide slopes and GPS can be used to provide good approach guidance to aircraft making fully automatic approaches to touchdown [ABSTRACT FROM PUBLISHER]

Evaluates a prototype microwave imaging system for its ability to recover two-dimensional electrical property distributions under transverse magnetic illumination using multitarget tissue equivalent phantoms. Image reconstructions as quantitative with respect to geometrical factors and electrical composition; Error rates.

In the diffraction region of a microwave landing system (MLS) elevation guidance. the field strength fluctuates due to such objects as buildings and hence the measuring error increases. This paper describes experiments to determine the effect of diffraction caused by the upper edges of a building. The results show that the field has a typical diffraction characteristic which can be calculated by regarding the building as a knife edge. It was found that the diffraction error cannot be ignored when measuring an angle, since the scanning beam is sharp in the vertical direction and flat in the horizontal direction. Hence, both the component proportional to the amplitude of the diffraction wave and that proportional to the partial differentiation of its incident angle (slope diffraction component) increase. It was found also that the measurement error characteristic around the shadow boundary, calculated by using the uniform geometrical theory of diffraction taking account of the slope diffraction, agrees well with the observational results. Generally, this method can be applied to the diffraction field strength and its measuring error estimation such as hangers. [ABSTRACT FROM AUTHOR]

Provides information on a study that described a synthetic vision system (SVS) for aid in landing aircraft in poor weather conditions. System overview; Details of the signal and display processing; Performance results of the SVS.

The Joint Precision Approach Landing System (JPALS) addresses tropospheric errors through double-difference and tropospheric model correction. Large residuals occur with two types of tropospheric anomalies: the vertical duct and horizontal non-nominal troposphere. Through analyzing 8 years of meteorological data from the European Center for Medium-Range Weather Forecasts (ECMWF), we find that the two types of anomalies can occur simultaneously. In addition, the existing vertical protection level (VPL) calculation method under tropospheric anomalies is based on the least squares method, which is not applicable to Sea-Based JPALS using the Kalman filter. Therefore, we start by calculating the zenith duct error by numerical integration. The maximum error observed is 45.64 mm, and the error seasonal characteristic is analyzed. For the non-nominal troposphere, the worst meteorological conditions in the Chinese surrounding sea areas are used to calculate the non-nominal errors, which are fitted to a satellite-elevation-dependent model. Then, a VPL calculation method based on the Kalman filter under tropospheric anomalies is proposed. Finally, a multiple approach simulation is conducted. The results show that the average VPL increments introduced by the duct and non-nominal troposphere anomalies are 0.082 m and 0.211 m, respectively, with growth percentages of 12.903% and 30.857%, respectively. The increment under simultaneous anomalies is 0.272 m with a growth of 40.427%. Furthermore, the average availability under normal conditions is 100%. Considering the duct and the non-nominal troposphere anomalies, the availability loss is 0.017% and 3.674%, respectively. Under simultaneous anomalies, this loss is 4.743%. [ABSTRACT FROM AUTHOR]