Terrain Reflections Research Articles

MASK IMPORTANCE IN BURNED AREA MAPPING BASED ON REMOTE SENSING, GIS AND OPEN-SOURCE PRODUCTS

Abstract. Forest and field fires are an increasing problem for EU countries located in the southern parts of Europe. With each passing day, the need to develop a technological scheme for monitoring the territories affected by fires and the timely provision of open data in order to recover damages is increasing.In this study, the method used to study burned areas is based on the analysis of multispectral satellite images, the differences in terrain reflectivity and the use of indices to highlight the differences between areas with healthy vegetation and burned areas, taking into account their different signatures. Open source software - SNAP, QGIS, images from Sentinel-2 with bands in the green, red, near-infrared and short-wave infrared spectral bands were used for the purposes of the research. Data from the Inspire Directive was also used to analyze the types and characteristics of affected areas.In many cases, water bodies show a similar difference as the Normalized Burn Ratio (NBR) index, for this reason the need for their preliminary masking arises. Clouds that appear in each input image are also masked. A combined water and cloud mask is applied. To detect the water bodies, NDWI was used to maximize the reflectance of the water body in the green band and minimize the reflectance of the water body in the NIR range.

Target Height Measurement under Complex Multipath Interferences without Exact Knowledge on the Propagation Environment

This paper investigates the direction-of-arrival (DOA) estimation-based target localization problem using an array radar under complex multipath propagation scenarios. Prevalent methods may suffer from performance degradation due to the deterministic signal model mismatch, especially when the exact knowledge of a propagation environment is unavailable. To cope with this problem, we first establish an improved signal model of multipath propagation for low-angle target localization scenarios, where the dynamic nature of convoluted interferences induced by complex terrain reflections is taken into account. Subsequently, an iterative implementation-based target localization algorithm with the improved propagation model is proposed to eliminate the detrimental effect of coherent interferences on target localization performance. Compared to existing works, the proposed algorithm can maintain satisfactory estimation performance in terms of target location parameters, even in severe multipath interference conditions, where the decorrelation preprocessing and accurate knowledge about the multipath propagation environment are not required. Both simulation and experimental results demonstrate the effectiveness of the proposed propagation model and localization algorithm.

Evaluation of TROPOMI and OMI Tropospheric NO2 Products Using Measurements from MAX-DOAS and State-Controlled Stations in the Jiangsu Province of China

The tropospheric vertical column density of NO2 (Trop NO2 VCD) can be obtained using satellite remote sensing, but it has been discovered that the Trop NO2 VCD is affected by uncertainties such as the cloud fraction, terrain reflectivity, and aerosol optical depth. A certain error occurs in terms of data inversion accuracy, necessitating additional ground observation verification. This study uses surface NO2 mass concentrations from the China National Environmental Monitoring Center (CNEMC) sites in Jiangsu Province, China in 2019 and the Trop NO2 VCD measured by MAX-DOAS, respectively, to verify the Trop NO2 VCD product (daily and monthly average data), that comes from the TROPOspheric Monitoring Instrument (TROPOMI) and Ozone Monitoring Instrument (OMI). The results show that the spatial distributions of NO2 in TROPOMI and OMI exhibit a similar tendency and seasonality, showing the characteristics of being high in spring and winter and low in summer and autumn. On the whole, the concentration of NO2 in the south of Jiangsu Province is higher than that in the north. The Pearson correlation coefficient (r) between the monthly average TROPOMI VCD NO2 and the CNEMC NO2 mass concentration is 0.9, which is greater than the r (0.78) between OMI and CNEMC; the r (0.69) between TROPOMI and the MAX-DOAS VCD NO2 is greater than the r (0.59) between OMI and the MAX-DOAS. As such, the TROPOMI is better than the previous generation of OMI at representing the spatio-temporal distribution of NO2 in the regional scope. On the other hand, the uncertainties of the satellite products provided in this study can constrain regional air quality forecasting models and top-down emission inventory estimation.

How Forward‐Scattering Snow and Terrain Change the Alpine Radiation Balance With Application to Solar Panels

AbstractRough terrain in mid‐ and high latitudes is often covered with highly reflective snow, giving rise to a very complex transfer of incident sunlight. In order to simplify the radiative transfer in weather and climate models, snow is generally treated as an isotropically reflecting material. We develop a new model of radiative transfer over mountainous terrain, which considers for the first time the forward scattering properties of snow. Combining ground‐measured meteorological data and high resolution digital elevation models, we show that the forward scattering peak of snow leads to a strong local redistribution of incident terrain reflected radiation. In particular, the effect of multiple terrain reflections is enhanced. While local effects are large, area‐wide albedo is only marginally decreased. In addition, we show that solar panels on snowy ground can clearly benefit from forward scattering, helping to maximize winter electricity production.

Discrete representation of terrain reflections for land clutter simulation

The formation of a discrete terrain model is one of the tasks of simulation of land clutter simulation using digital modeling methods. The smaller the sampling step is, the fewer calculations are needed to recreate the echo signal. On the other hand, too large the step leads to significant errors in the parameters of a simulated signal. The article considers the task of determining the necessary sampling step provided that the signals are simulated with a given accuracy. The approach proposes the analysis of the dispersion and autocorrelation function of the signal at the output of the matched filter of the radar station receiver that is obtained by transmitting a simulated echo signal to receiver input. The expressions are obtained for calculating the sampling frequency depending on the distribution properties of terrain reflections and the probing signal parameters. They can be used to build terrain models for echo signal simulation.

Research on the burst height measurement method based on the missile-borne millimeter wave detector

A millimeter wave detector is applied to a novel large dynamic optional burst height proximity fuze, and it provides a higher measurement precision. In this paper, the height measurement model of the missile-borne millimeter wave detector is established to provide a theoretical basis for the measurement of burst height. A burst height measurement method based on the change rate of voltage and Doppler shift has been proposed. Compared with the traditional millimeter wave fuze continuous wave height measurement system, the proposed method shows higher measurement accuracy and faster computing speed. Through a series of digital simulation experiments, the proposed method allows the height to be estimated when the terrain reflectivity is unknown.

Simulation and design of active control systems for acoustic pulse noise

Active noise control (ANC) techniques have been successfully investigated and implemented for the attenuation of stationary acoustic noise. Furthermore, adaptive methods for impulsive noise have been also presented in the literature, even though the considered statistical models are well suited only for a narrow class of impulsive disturbances that can be faced in realistic scenarios. In this paper, a preliminary study addressing the design of a non-adaptive deterministic ANC system for pulse signals is developed by avoiding any statistical assumption. The theory of Wave Field Synthesis is explicitly exploited in a destructive manner, that is, generating a canceling acoustic pressure field by means of arrays of secondary sources. An ad-hoc interactive software simulator implementing the proposed approach is realized and used to virtually explore the solution spaces of some test case scenarios. Simulations’ results considering linear and planar arrays in the case of free space propagation, as well as in the case of interaction with a hard ground, are presented and compared. Furthermore, the impact of different design solutions proposed to mitigate the impairments due to terrain reflections is evaluated.

SAR Image Despeckling Via Structural Sparse Representation

A novel synthetic aperture radar (SAR) image despeckling method based on structural sparse representation is introduced. The proposed method utilizes the fact that different regions in SAR images correspond to varying terrain reflectivity. Therefore, SAR images can be split into a heterogeneous class (with a varied terrain reflectivity) and a homogeneous class (with a constant terrain reflectivity). In the proposed method, different sparse representation based despeckling schemes are designed by combining the different region characteristics in SAR images. For heterogeneous regions with rich structure and texture information, structural dictionaries are learned to appropriately represent varied structural characteristics. Specifically, each patch in these regions is sparsely coded with the best fitted structural dictionary, thus good structure preservation can be obtained. For homogenous regions without rich structure and texture information, the highly redundant photometric self-similarity is exploited to suppress speckle noise without introducing artifacts. That is achieved by firstly learning the sub-dictionary, then simultaneously sparsely coding for each group of photometrically similar image patches. Visual and objective experimental results demonstrate the superiority of the proposed method over the-state-of-the-art methods.

Influence of complex topography on global solar radiation in the Yangtze River Basin

Global solar radiation (GSR) is the most direct source and form of global energy, and calculation of its quantity is highly complex due to influences of local topography and terrain inter-shielding. Digital elevation model (DEM) data as a representation of the complex terrain and multiplicity condition produces a series of topographic factors (e.g. slope, aspect, etc.). Based on 1 km resolution DEM data, meteorological observations and NOAA-AVHRR remote sensing data, a distributed model for the calculation of GSR over rugged terrain within the Yangtze River Basin has been developed. The overarching model permits calculation of astronomical solar radiation for rugged topography and comprises a distributed direct solar radiation model, a distributed diffuse radiation model and a distributed terrain reflectance radiation model. Using the developed model, a quantitative simulation of the GSR space distribution and visualization has been undertaken, with results subsequently analyzed with respect to locality and terrain. Analyses suggest that GSR magnitude is seasonally affected, while the degree of influence was found to increase in concurrence with increasing altitude. Moreover, GSR magnitude exhibited clear spatial variation with respect to the dominant local aspect; GSR values associated with the sunny southern slopes were significantly greater than those associated with shaded slopes. Error analysis indicates a mean absolute error of 12.983 MJm−2 and a mean relative error of 3.608%, while the results based on a site authentication procedure display an absolute error of 22.621 MJm−2 and a relative error of 4.626%.

Height Estimation for Ballistic Platforms using Differential Measurements

Use of radio waves is a very common choice for proximity fuzes. The stand-off distance for fuzes varies between a lower and an upper limit depending on the electromagnetic reflectivity of terrain (target). If the reflectivity of the terrain is comparably higher, the return power at the receiver reaches to the threshold level more quickly and the stand-off distance increases. The work presented here introduces an approach to estimate the height of airborne ballistic platforms more precisely compared with the conventional fuzes regardless of the reflection properties of the terrain. Independent measurements of the rate of change of voltage from the receiver and the rate of change of height (from Doppler shift) allow the height to be estimated when the terrain reflectivity is unknown.

Shortwave radiation parameterization scheme for subgrid topography

Topography is well known to alter the shortwave radiation balance at the surface. A detailed radiation balance is therefore required in mountainous terrain. In order to maintain the computational performance of large‐scale models while at the same time increasing grid resolutions, subgrid parameterizations are gaining more importance. A complete radiation parameterization scheme for subgrid topography accounting for shading, limited sky view, and terrain reflections is presented. Each radiative flux is parameterized individually as a function of sky view factor, slope and sun elevation angle, and albedo. We validated the parameterization with domain‐averaged values computed from a distributed radiation model which includes a detailed shortwave radiation balance. Furthermore, we quantify the individual topographic impacts on the shortwave radiation balance. Rather than using a limited set of real topographies we used a large ensemble of simulated topographies with a wide range of typical terrain characteristics to study all topographic influences on the radiation balance. To this end slopes and partial derivatives of seven real topographies from Switzerland and the United States were analyzed and Gaussian statistics were found to best approximate real topographies. Parameterized direct beam radiation presented previously compared well with modeled values over the entire range of slope angles. The approximation of multiple, anisotropic terrain reflections with single, isotropic terrain reflections was confirmed as long as domain‐averaged values are considered. The validation of all parameterized radiative fluxes showed that it is indeed not necessary to compute subgrid fluxes in order to account for all topographic influences in large grid sizes.

Topographic Effects on the Surface Radiation Balance in and around Arizona’s Meteor Crater

Abstract The individual components of the slope-parallel surface radiation balance were measured in and around Arizona’s Meteor Crater to investigate the effects of topography on the radiation balance. The crater basin has a diameter of 1.2 km and a depth of 170 m. The observations cover the crater floor, the crater rim, four sites on the inner sidewalls on an east–west transect, and two sites outside the crater. Interpretation of the role of topography on radiation differences among the sites on a representative clear day is facilitated by the unique symmetric crater topography. The shortwave radiation balance was affected by the topographic effects of terrain exposure, terrain shading, and terrain reflections, and by surface albedo variations. Terrain exposure caused a site on the steeper upper eastern sidewall of the crater to receive 6% more daily integrated shortwave energy than a site on the lower part of the same slope. Terrain shading had a larger effect on the lower slopes than on the upper slopes. At the lower western slope site the daily total was reduced by 6%. Measurements indicate a diffuse radiation enhancement due to sidewall reflections. The longwave radiation balance was affected by counterradiation from the crater sidewalls and by reduced emissions due to the formation of a nighttime temperature inversion. The total nighttime longwave energy loss at the crater floor was 72% of the loss observed at the crater rim.

Radiosity Approach for the Shortwave Surface Radiation Balance in Complex Terrain

Abstract The influence of topography on the radiation balance in complex terrain has so far been investigated either with very simple or very sophisticated approaches that are limited, respectively, by an uncontrolled spatial representation of radiative fluxes or heavy computational efforts. To bridge this gap in complexity, this paper proposes the radiosity approach, well known in computer graphics, to study anisotropic reflections of radiation in complex terrain. To this end the radiosity equation is rederived in the context of three-dimensional radiative transfer. The discretized equation is solved by means of an adapted version of progressive refinement iteration. To systematically study terrain effects, the geometrical disorder provided by the topography is considered in its simplest approximation by Gaussian random fields. These model topographies capture the most important length scales of complex terrain, namely a typical elevation and a typical valley width via the variance and the correlation length of the field, respectively. The mean reflected radiation is computed as a function of these length scales and sun elevation, thereby explicitly addressing finite system sizes and grid resolutions. A comparison with an isotropic parameterization of terrain reflections reveals that mean values are similar whereas spatial distributions vary remarkably. It is also shown that the mean reflected radiation in real topography is reasonably well characterized by the Gaussian approximation. As a final application of the method, the effective albedo of a topography is shown to vary with sun elevation and domain-averaged albedo, leading to albedo differences up to 0.025.

Military route planning in battlefield simulation: effectiveness problems and potential solutions

Path searching is challenging problem in many domains such as simulation war games, robotics, military mission planning, computer generated forces (CGF), etc. Effectiveness problems in military route planning are related both with terrain modelling and path planning algorithms. These problems may be considered from the point of view of many criterions. It seems that two criterions are the most important: quality of terrain reflection in the terrain model and computational complexity of the on(off)-line path planning algorithm. The paper deals with two above indicated problems of route planning effectiveness. Comparison of approaches used in route planning is presented. The hybrid, terrain merging-based and partial path planning, approach for route planning in dynamically changed environment during simulation is described. It significantly increase effectiveness of route planning process. The computational complexity of the method is given and some discussion for using the method in the battlefield simulation is conducted. In order to estimate how many times faster we can compute problem for finding shortest path in network with n big squares (b-nodes) with relation to problem for finding shortest path in the network with V small squares (s-nodes) acceleration function is defined and optimized.

Multipath interferometry technique for airborne array calibration

A new technique is developed to compensate multiple-wavelength distortion in airborne antenna arrays. This approach exploits the phase information in microwave reflections from arbitrary terrain. To handle reflections incident over a broad angle, a range-Doppler preprocessor is used in each element channel to resolve wavefronts incident simultaneously from different directions. The phase information for each direction of arrival is compared between elements and processed by optimal estimators to determine the phase corrections needed to compensate the distortion. To develop the estimators, a statistical model of the complex baseband terrain reflections is developed. This is in turn used to generate conditional probability densities involving the range Doppler observations and the parameters to be estimated. These densities are subsequently used to develop minimum variance and maximum likelihood estimators. The new estimators use additional information that has not been exploited by previous techniques and therefore provide enhanced performance.

Reduction of layover distortion in SAR imagery

Layover distortion in synthetic aperture radar (SAR) imagery is interpreted as the result of the inability of an obliquely oriented remote sensor to distinguish the horizontal and vertical components of its range measurement. A geometric model of the SAR imaging process is employed in conjunction with digital terrain elevation data to simulate the layover distortion inherent in a Seasat SAR image of a mountainous scene. The simulated layover database is then used to solve the inverse imaging problem, which is to reduce layover distortion by geographically redistributing concentrations of the SAR image amplitude that can be attributed to the focusing influence of mountain slopes that face the radar. Cross-correlation and classification statistics are used to compare the results with an aerial photograph. Two classes of terrain are distinguished. These correspond to positive and negative correlations of radar and optical reflectivities for different surface textures. They also correspond to higher and lower scene elevations. These two classes of terrain reflectivity are misregistered by about 160 m along the SAR track and are separated by about 60 m in mean elevation. The misregistration is shown to be consistent with the clutterlock and autofocus procedures employed by the SAR scene correlator as it responds to the variance in the earth's relative rotational velocity over the three-dimensional terrain.

Diffuse solar radiation—Daily and monthly values as affected by snow cover

It is generally recognized that surface albedo (terrain reflectance) has a significant effect on the diffuse fraction of global radiation. In colder climates, ground snow cover could be expected to alter the terrain reflectance significantly. The objective of this paper was to study the effect of ground snow cover on the diffuse fraction of the daily and the monthly average global radiation and to develop empirical relationships which would permit the calculation of the diffuse solar component.

Review Article Radiometric correction of visible and infrared remote sensing data at the Canada Centre for Remote Sensing

Abstract This article reviews experience in radiometric corrections of satellite and airborne remote sensing data at the Canada Centre for Remote Sensing (CCRS) during the period 1972 to 1986. It also describes current research areas and recommends areas of future research where high priority is important for global change monitoring and for the derivation of quantitative information from remotely-sensed data in the solar reflective spectral regions. Throughout its history, CCRS has directed its efforts towards meeting specific needs. For satellite data (Landsat MSS, Thematic Mapper, AVHRR, and now SPOT HRV), the progression has been from relative calibration of detector elements (destriping) to absolute radiometric calibration of digital data. The routine use of atmospheric corrections and a priori knowledge of terrain reflectance properties have been introduced into the generation of specialized digital enhancements for photographic products. This has required the investigation of a wide range of radiom...

Automated measurements of terrain reflection and height variations using an airborne infrared laser system

Abstract A pulsed near-infrared laser system was converted to determine laser height and reflection values in airborne operations. The laser produces precise traces of the terrain and vegetation canopy and tree measurements can readily be made in open forests since the laser beam frequently penetrates openings in the canopy cover. The reflection measurements were useful in discriminating between vegetation type and density. Using the combined laser height, laser reflection and reflection variability parameters, it was possible to arrive at a simple semiautomated terrain classification which allowed a distinction between conifer and broadleaf forests and terrain with low-growing vegetation cover. The classification of individual trees into coniferous and broadleaf of different height classes is demonstrated. The data is in digital form and can be incorporated into geographic information systems. Considering that these measurements were made at a single wavelength (904 nm), it is clearly evident that high-r...

Effect of terrain orientation and solar position on satellite-level luminance observations

Changes in the luminance of a terrain along the local nadir direction are studied as a function of terrain slope, and the solar azimuth and elevation angles. The digital terrain data for the Santa Clara valley-Mt. Hamilton region of California, available from the U.S. National Cartographic Information Center, are used for this purpose. The elevation above mean sea-level of this selected region varies between 24 and 1,282 m. Luminance computations are performed by assuming the Lommel-Seeliger law of reflection, and the terrain reflectance to be a constant and independent of its geographic location. The atmospheric effects and contributions due to multiple reflections are neglected. It is shown that the ratio of the actual terrain luminance to that for the corresponding flat surface for 64 equal-size (∼ 4 km 2) finite subregions, changes by a very significant amount over the selected region, and also with changes in the solar position. Selected Landsat MSS band 7 data of the same region are presented for validation purposes.