Board Unmanned Aerial Vehicles Research Articles

Estimation of the spatial resolution of a synthetic aperture radar antenna of the VHF frequency range placed on board an unmanned aerial vehicle along a real flight path

Background. Currently, there is an intensive development of radar systems for remote sensing of the Earth, including those placed on unmanned aerial vehicles. Synthetic aperture radars are an effective means of round-the-clock and all-weather observation of objects on the Earth’s surface. Radars operating in the VHF range allow you to observe hidden and subsurface objects. The need for practical implementation of VHF band radar with synthesizing the aperture on board unmanned aerial vehicles requires additional research on the spatial resolution of radars, taking into account the unstable trajectory of the carrier. Aim. The article considers the analysis of the influence of the flight path and its measurement errors on the quality of the radar image. Methods. The research method provides an analysis of the shape of the radar uncertainty function with the synthesis of an aperture, which was built along a real trajectory using semi-natural mathematical modeling. Results. As a result of the conducted research, it is shown that the quality of radar images is influenced not only by errors in the knowledge of motion parameters, but also by the very nature of the carrier’s movement and the duration of the flight. Conclusion. Based on the results of field tests, it turned out to be possible to analyze these factors and determine the requirements for the UAV navigation system. Thus, the article shows the possibility of quality control of VHF band radar with synthesized aperture placed on board a UAV.

ДВУХПОЗИЦИОННЫЙ ГЕОРАДИОЛОКАТОР НА БПЛА ДЛЯ ОПЕРАТИВНОГО МОНИТОРИНГА ПОДПОВЕРХНОСТНЫХ ВОДНЫХ РЕСУРСОВ

This paper considers the implementation of a two-position ground penetrating radar (GPR) located on board unmanned aerial vehicles (UAVs) and designed for the operational search for groundwater in arid and desert regions of Mongolia, which is an extremely urgent task. With the help of synthesizing the GPR antenna aperture on the UAV, a significant increase in information content is achieved compared to existing GPRs, since it becomes possible to obtain a panoramic radar image of the subsurface layers of the probed medium with the required resolution with a sufficiently wide swath. On the other hand, the necessary efficiency (required, for example, when monitoring vast desert areas) can only be achieved with a sufficiently wide field of view created on the basis of the two-position sounding principle, where the emitting and receiving signals are formed and processed on UAVs of different or equal heights flying with the same speed and spaced orthogonally to the direction of their movement, which makes it possible to use quasi-mirror reflection. In this case, the swath will be noticeably larger than in the case of nadir sounding. In a condensed form, the article considers the following issues: the model of a subsurface aquifer, the geometry of a two-position GPR in the quasi-mirror sounding mode, up to the features of synthesizing the aperture (Doppler narrowing of the radiation pattern) of the receiving antenna, resolution, the required potential of a two-position GPR for reliable detection of an aquifer subsurface horizon, accuracy measurements of its depth, as well as the need for experimental work to test the theoretical provisions.

Assessment of vineyard vigour and yield spatio-temporal variability based on UAV high resolution multispectral images

Accurate, timely assessment of the vineyard on a field scale is essential for successful grape yield and quality. Remote sensing can be an effective and useful monitoring tool, as data from sensors on board Unmanned Aerial Vehicles (UAV) can measure vegetative and reproductive growth and thus directly or indirectly detect variability. Through the images obtained from UAV, the Vegetation Indices (VIs) can be calculated and compared with various agronomic characteristics of the vineyard. The objective of this study was to evaluate the multispectral response of the vineyard in three specific phenological phases and to analyse the spatial distribution of vegetative vigour. A multirotor UAV equipped with a camera featuring multispectral sensors was used. Four VIs namely Normalised Difference Vegetation Index (NDVI), Normalised Difference Red Edge (NDRE), Green Normalised Difference Vegetation Index (GNDVI), Modified Soil Adjusted Vegetation Index (MSAVI), were calculated using the georeferenced orthomosaic UAV images. Computer vision techniques were used to segment these orthoimages to extract only the vegetation canopy pixels. High level of agronomic variability within the vineyard was identified. Pearson's coefficient showed a significant correlation between NDVI and NDRE indices and yield since early phenological stages (r = 0.80 and 0.72 respectively), GNDVI at grape ripening (r = 0.83). Shoot pruning weight (SPW) shows the highest values of correlation (r = 0.84) with NDVI during the phenological stage of berries pea size. Simple linear regression techniques were evaluated using VIs as predictors of the SPW, and accurate predictive results were obtained for NDVI and NDRE with RMSE values of 0.18 and 0.24, respectively. Geostatistical analysis was applied to model the spatial variability of SPW, and thus vineyard vigour. Assessing spatial variability and appreciating the level of vigour enables improved vineyard management by increasing sustainability and production efficiency.

Solar UAVs—More Aerodynamic Efficiency or More Electrical Power?

Solar UAVs (unmanned aerial vehicles) have experienced important development in recent years. The use of solar free energy is not neglected in the present energy crisis, with the intention to move toward green energies. However, an important problem arises concerning the limited amount of solar energy available on board UAVs. Until now, high-aerodynamic-efficiency configurations have been used. These configurations use high-aspect-ratio wings. However, high-aspect-ratio wings have some disadvantages regarding their excessive elasticity and weak bending resistance in the housing section. Additionally, the aircraft maneuverability is reduced. In this work, a study is proposed on a solar UAV configuration that sacrifices high aerodynamic efficiency for a higher surface area available for solar cells. In this manner, the amount of energy available on board the UAV is increased, and the UAV structure becomes more rigid and robust. The presented UAV fits better with more complex evolutions, is more maneuverable and the wingspan is much reduced. This UAV is more compact, can maneuver better in the take-off and landing phases, and the necessary storage space is considerably reduced. This paper highlights the performances that can be achieved using this kind of UAV and explores whether these performances are enough for some applications. Using an on-board energy balance, the possible performances of this new configuration is studied. As this is a preliminary study, the precision level is not very high, but it offers an image concerning the possibilities of this new configuration.

Transmission quality evaluation of multistreaming video data from the UAV to the ground station in network simulator 3 simulation environment using WI-FI standards

The article presents the results of transmitting video data simulation in real time from video cameras on board Unmanned Aerial Vehicles (UAVs) to a ground station (GS). The main purpose of the article was to evaluate the impact of the flying source node number on Quality of Service (QoS) metrics, such as Packet Delivery Ratio and Goodput at OSI model application layer. A scenario was considered when hovering over UAVs, in the zone of reliable communication, transmitted a stream of video data to a ground station, then the distance between the UAV and the GS increased to repeat the experiment. The bitrate was maintained at the same level, close to the bitrate of real high-definition video. The experiment was carried out in the Network Simulator 3 (NS-3) simulation environment for scenarios with one, two, four, and eight source nodes. Simulation results have shown the negative impact of the increasing the number of flying source nodes on Quality of Service (QoS) metrics such as Packet Delivery Rate (PDR) and Goodput. Recommendations regarding the applicability of different standards of the 802.11 family to scenarios for using UAVs in the multistreaming video data transmission mode are given. A change in the relationship of useful throughput on the number of source nodes by 15 % was also found.

Citrus orchards under formation evaluated by UAV-Based RGB Imagery

Few studies have investigated the biometric attributes of citrus orchards under formation that use RGB sensors on board unmanned aerial vehicles (UAV) and the challenges are great. This study aimed to develop and validate a method of using aerial UAV images by automated routines to evaluate the biometric attributes of a crop of ‘Tahiti’ acid lime under formation. We used a multirotor UAV, programmed to capture images at three different map scales, with a frontal and side overlap of 80 %. Geoprocessing was carried out both with and without ground control points on each scale. An automated routine was developed in an open-source environment, consisting of three processing phases: i) Estimation of the plant biometric attributes, ii) Statistical analysis, and iii) Statistical Report Map (SRM). The use of the developed routine allowed to delimit and estimate the crown projection area with an accuracy of more than 95 % as well as identify and quantify the plants with an accuracy of over 97 %. The use of ground control points during the processing stage does not increase accuracy in estimating the biometric attributes under evaluation. On the other hand, map scale is strongly correlated with the quality of the estimates, especially plant height. The results allowed to define a method for the acquisition and analysis of aerophotogrammetric data using a UAV, which can be used to measure the plant biometric attributes under analysis and the method can be easily adapted to perennial crops.

Reinforcement Learning Aided UAV Base Station Location Optimization for Rate Maximization

The application of unmanned aerial vehicles (UAV) as base station (BS) is gaining popularity. In this paper, we consider maximization of the overall data rate by intelligent deployment of UAV BS in the downlink of a cellular system. We investigate a reinforcement learning (RL)-aided approach to optimize the position of flying BSs mounted on board UAVs to support a macro BS (MBS). We propose an algorithm to avoid collision between multiple UAVs undergoing exploratory movements and to restrict UAV BSs movement within a predefined area. Q-learning technique is used to optimize UAV BS position, where the reward is equal to sum of user equipment (UE) data rates. We consider a framework where the UAV BSs carry out exploratory movements in the beginning and exploitary movements in later stages to maximize the overall data rate. Our results show that a cellular system with three UAV BSs and one MBS serving 72 UE reaches 69.2% of the best possible data rate, which is identified by brute force search. Finally, the RL algorithm is compared with a K-means algorithm to study the need of accurate UE locations. Our results show that the RL algorithm outperforms the K-means clustering algorithm when the measure of imperfection is higher. The proposed algorithm can be made use of by a practical MBS–UAV BSs–UEs system to provide protection to UAV BSs while maximizing data rate.

Autonomous fire-fighting with heterogeneous team of unmanned aerial vehicles

This paper addresses autonomous fire-fighting missions with a heterogeneous team of Unmanned Aerial Vehicles (UAVs). We use UAVs with different capabilities to extinguish cooper- atively fires on the ground and on facades of high-rise buildings. The former is done by deploying fireproof blankets, whereas a water-jet system is used to extinguish fires on building facades. First, we propose two novel mechanisms on board UAVs for fire extinction: a system to deploy a blanket on the ground automatically, and a device to shoot water at facade fires. Then, we describe our software architecture for cooperative multi-robot missions in outdoor and unstructured environments, where robustness and reliability play a key role. The system was particularly developed for the Mohamed Bin Zayed International Robotics Challenge (MBZIRC), where we achieved the best performance in the fire-fighting Challenge. However, the conceptual design of our extinguishing devices and our software architecture are more general and could be applied to other search and rescue situations. We present not only our results in the final stage of MBZIRC but also our simulations and field experiments throughout the months previous to the competition, during which we assessed our system and tuned its performance.

Noncontact Vital Sign Detection With UAV-Borne Radars: An Overview of Recent Advances

Airborne radar carried on board unmanned aerial vehicles (UAVs) is serving as the harbinger of new remote sensing applications for security and rescue in inclement environments. The mobility and agility of UAVs, along with intelligent onboard sensors (cameras, acoustics, and radar), are more effective during the early stages of disaster response. The ability of radars to penetrate through objects and operate in low-visibility conditions enables the detection of occluded human subjects on and under debris when other sensing modalities fail. Recently, radars have been deployed on UAVs to measure minute human physiological parameters, such as respiratory and heart rates while sensing through clothing and building materials. Signal processing techniques are critical in enabling UAV-borne radars for human vital sign detection (VSD) in multiple operation modes. UAV radar interferometry provides valuable VSD in both hovering and flying motions. In the synthetic aperture radar (SAR) configuration, UAV-based VSD is available at a high spatial resolution. Novel radar configurations, such as in through-material sensing, UAV swarm, and tethered UAVs, are required to penetrate obstacles, facilitate multitasking, and allow for high endurance, respectively. This article provides an overview of the recent advances in UAV-borne VSD, with a focus on the deployment modes and processing methods.

Detection and mapping of trees infected with citrus gummosis using UAV hyperspectral data

Monitoring citrus diseases and pests in early stages is fundamental to ensure the efficiency of phytosanitary control and plant health. The various diseases caused by fungi, bacteria, viruses, and pests limit citrus production. Citrus gummosis disease, caused by the fungus Phytophthora spp., is the main fungal disease of citrus in Brazil. The lesions caused to the trunk and roots by Phytophthora spp. lead losses in production, foot and root rot, brown fruit rot, canopy discoloration and leaf yellowing. Remote sensing is a nondestructive detection technology, that has been used to detect phytosanitary problems in agricultural crops. Multi and hyperspectral sensors on board unmanned aerial vehicles (UAVs) have been extensively applied in agriculture. In this study, the capability for the detection of citrus gummosis was evaluated in two data sets. The first one considered hyperspectral images acquired with a 25 band sensor covering a spectral range from 500 nm to 840 nm, and the second data set was a simulated 3 band of multispectral sensor. The results indicated a better performance for the detection of citrus gummosis with the hyperspectral images than with three bands multispectral images. The high dimensionality of the hyperspectral data and the detailed spectral information allowed a more accurate classification of citrus gummosis infected plants. The classification maps were validated with field data and achieved an accuracy of 0.79 (F-score = 0.55) for the health map produced with multispectral data and an accuracy of 0.94 (F-score = 0.85) for the health map produced by the hyperspectral data.

Improved In-Flight Estimation of Inertial Biases through CDGNSS/Vision Based Cooperative Navigation.

This paper discusses the exploitation of a cooperative navigation strategy for improved in-flight estimation of inertial sensors biases on board unmanned aerial vehicles. The proposed multi-vehicle technique is conceived for a “chief” Unmanned Aerial Vehicle (UAV) and relies on one or more deputy aircrafts equipped with Global Navigation Satellite System (GNSS) antennas for differential positioning which also act as features for visual tracking. Combining carrier-phase differential GNSS and visual estimates, it is possible to retrieve accurate inertial-independent attitude information, thus potentially enabling improved bias estimation. Camera and carrier-phase differential GNSS measurements are integrated within a 15 states extended Kalman filter. Exploiting an ad hoc developed numerical environment, the paper analyzes the performance of the cooperative approach for inertial biases estimation as a function of number of deputies, formation geometry and distances, and absolute and relative dynamics. It is shown that exploiting two deputies it is possible to improve biases estimation, while a single deputy can be effective if changes of relative geometry and dynamics are also considered. Experimental proofs of concept based on two multi-rotors flying in formation are presented and discussed. The proposed framework is applicable beyond the domain of small UAVs.

Розроблення аерознімального комплексу на основі БПЛА октокоптера DJI S100

Goal. The purpose of the work is to develop an aerial photography complex based on a DJI S1000 helicopter UAV for aerial photography, which includes a laser scanner (LS) and a digital camera (CPC). Method. For several decades, aerial photography has been an effective tool for geodetic works, geophysical surveys and various types of monitoring. On the other hand, the use of not only digital imaging, but also laser scanning of objects allows to maximize the accuracy of obtaining the coordinates of points on the ground and eliminate such a process as plan-height binding in the field, which occupies more than 80 % of field work that is, much cheaper the process of creating cartographic materials. In addition, the use of laser scanners on board unmanned aerial vehicles helps to solve a number of scientific and applied problems in various fields, such as engineering research, environmental monitoring, landscape research and modeling, construction, architecture, archeology and more. Comprehensive study, research and monitoring of the environment involves the availability and use of highly efficient modern technologies, special software for data processing and analysis and qualified human resources. Aerial laser scanners are the latest high-precision technology for obtaining data about the object by noncontact method and have a multi-purpose purpose. I have been actively using them in the world since the early 2000s. They have a number of advantages over traditional aerial photography. Drugs are manufactured by the world’s leading companies, they are available on the market and are in great demand among foreign specialists. Unfortunately, in Ukraine, airborne laser scanners are used in limited quantities to perform special tasks with the involvement of foreign experts. In this area we have a significant lag compared to other European countries. Therefore, the acquisition and application of such a software and technology complex and UAV will help solve and accelerate the solution of many important scientific and applied problems in Ukraine, as well as increase the potential, opportunities and prestige in domestic and world science and practice. Results. A mock-up model of installation and implementation of Velodyne VLP-16 on a DJI S1000 helicopter UAV has been developed. The authors analyzed the known systems and created the best option for connecting and connecting the elements, which made it possible to simplify the layout of the devices, which in turn made it possible to reduce the cost of the proposed complex. Scientific novelty and practical significance. For the first time in Ukraine, a method of installing a helicopter-type UAV was developed and proposed. With the help of an airborne laser scanning system installed on board an unmanned aerial vehicle of helicopter type it is possible to solve a number of important scientific and applied tasks, such as: monitoring the technical condition of large and hard-to-reach structures – nuclear, hydro and thermal power plants, power lines, etc. ; monitoring the condition of roads, detecting places of surface damage and other dangerous places in order to prevent car accidents; detection of damage to forests and agricultural lands; observation and prevention of landslides in mountains and industrial quarries, places of soil erosion; monitoring of water resources, changes in contours and heights of the coastal strip; detection of roof defects, deformations, wall cracks on highrise buildings for architectural measurements, 3D modeling, documentation and preservation of cultural heritage sites; assistance in archaeological exploration to identify archaeological sites and study artifacts. In addition, peripheral drugs can be installed on other moving objects (cars, railcars, boats, etc.) and scanning from fixed bases in stationary conditions.

Monitoring of the Hydrological Situation Along Pipeline Routes by Means of Microwave Radiometry Methods

The possibility of using passive microwave remote sensing technologies to monitor the hydrological situation along pipeline routes, including oil and gas pipelines, is being considered. The possibility of detecting potentially dangerous sections along pipeline routes, dams, railways and highways is shown to assess risky situations. Existing and prospective scanning and trace microwave radiometric systems capable of solving this problem are described. The main technical characteristics of existing and new radiometric systems are given. The advantages of using radiometric monitoring tools on board unmanned aerial vehicles are considered.

Метод локального моніторингу атмосфери за допомогою безпілотних літальних апаратів

Theoretical substantiation of the method of organization of tropospheric monitoring by means of unmanned aerial vehicles with means of atmospheric monitoring installed on board as an auxiliary technical element of the method of organization of atmospheric monitoring by automated stations located on the basis of base stations of mobile operators is carried out. The analysis of liquidations of consequences of resonant accidents, and also designs and characteristics of unmanned aerial vehicles used at their liquidation is carried out. Modern types and characteristics of measuring equipment that can be installed on board unmanned aerial vehicles and used in atmospheric monitoring are considered. An algorithm for tropospheric monitoring has been developed, based on the use of unmanned aerial vehicles with state monitoring devices installed on board, for the operation of which the time during which measurements should be performed, as well as the required number and coordinates of concentration measurement points have been determined. Differs from existing solutions to the problem of determining the coordinates of measurement points using genetic algorithms. Also, the developed method of local monitoring of the atmosphere with the help of unmanned aerial vehicles equipped with means of monitoring the state of the atmosphere took into account the information delay and determined the time interval during which it is possible to perform measurements. The results obtained in the work are of most interest to the rescue services, which plan to use unmanned aerial vehicles to monitor the state of the atmosphere in emergencies, accompanied by emissions of pollutants into the atmosphere.

Analysis of the military application of unmanned aircraft and main direction for their development

Modern military unmanned aerial vehicles (UAVs) are assigned a wide range of functions, for the implementation of which they perform many tasks in various military conflicts. The results of the analysis give them the opportunity to reveal the problems in the use of UAVs, make changes in their functions and tasks and identify areas for further development. At present, this requires the introduction of the achievements of artificial intelligence, the introduction of expert systems and microelectronics on board UAVs, as well as their integration with various other means of conducting armed struggle. At the same time, some of the technological solutions for the creation and improvement of UAVs for military purposes can be applied in the civilian sector.

Application of active methods hyperspectral survey for remote monitoring of oil pipeline systems

The development of mankind is characterized by an intensive increase in the anthropogenic load on the environment, which in turn can lead to a deterioration of the ecological balance in the ecosystem and affect the life and health of people. Purpose. The purpose of this work is to analyze methods of environmental and technical monitoring of main oil pipeline systems. Task. To analyze and make a comparative analysis of active methods of hyperspectral survey and other modern existing remote methods of environmental and technical monitoring of main oil pipeline systems in order to obtain the most complete information about the occurrence of dangerous and emergency situations. Research result. Hyperspectral survey, in comparison with other monitoring methods, allows you to identify objects by their physical and chemical composition, determine and analyze the species composition and state of vegetation, the geological structure of territories, study the chemical and physical composition, and so on. On the other hand, the amount of data that has to be processed, filtered, transmitted through communication channels, stored, and classified is very large. This, in turn, leads to limited data processing capabilities of hyperspectral images both on Board unmanned aerial vehicles (UAVs), and the complexity of data processing in ground-based data collection points. Scientific novelty. Hyperspectral survey is an advanced multispectral survey and is the most modern method for monitoring oil pipelines. Thanks to the latest technologies, the number of spectral channels increases from tens to hundreds or even thousands. The advantages of using this method are defined. Conclusions and practical significance. The use of active hyperspectral survey methods for remote monitoring of oil pipeline systems is a promising means of preventing and eliminating accidents at oil transport facilities, but it requires solving some technical problems. However, after their solution, these monitoring methods will be applied not only in the field of safety of oil transportation facilities and the study of the environmental condition of territories in the event of accidents at these facilities, but also in other areas of environmental, geological, agricultural and technical monitoring.

Szorstkość pokrycia terenu jako źródło błędu metody SfM zastosowanej do rekonstrukcji zasięgu pokrywy śnieżnej = Terrain roughness as a source of error with the SfM method applied to the reconstruction of snow cover extent

A comparison between errors associated with snow-cover reconstruction performed by processing aerial imagery acquired by a visible-light camera mounted on board unmanned aerial vehicles, one the one hand; and average terrain roughness, on the other, revealed a dependent relationship between these variables. A stronger correlation is noted for two of the studied test areas (Polana Izerska and Krobica, both located in SW Poland), as opposed to the remaining site (Drożyna, SW Poland). In particular, correlations are noticeable where the analysis is performed in moving windows. It is typical for terrain where depth of snow cover is reconstructed with severe errors to reveal a high degree of roughness caused by single trees, clumps of trees or buildings. Ambiguous results are obtained for the Drożyna research field. While the character of the dependent relationship there seems consistent with results for the remaining sites, the strength is low. The lower values for the correlation coefficient were driven by observations for which errors were found to be high while values for the Topographic Ruggedness Index were at the same time low. This effect can be explained by reference to the specific nature of the area reconstructed, which is much transformed by human activity. It proves difficult to reconstruct the depth of snow cover on roads properly, as these are either partially cleared or snow or characterised by its loss in the course of melting. Low thickness of snow cover is thus found to be a constrained when it comes to the generation of accurate reconstructions of the depth of snow cover. This is in fact a finding in agreement with what has been reported by other authors.

Developing Inspection Methodology of Solar Energy Plants by Thermal Infrared Sensor on Board Unmanned Aerial Vehicles

Photovoltaic (PV) power generation facilities have been built on various scales due to rapid growth in response to demand for renewable energy. Facilities built on diverse terrain and on such a scale are required to employ fast and accurate monitoring technology for stable electrical production and maintenance. The purpose of this study was to develop a technology to analyze the normal operation and failure of solar modules by acquiring images by attaching optical and thermal infrared sensors to unmanned aerial vehicles (UAVs) and producing orthographic images of temperature information. The results obtained in this study are as follows: (1) a method of using optical and thermal infrared sensors with different resolutions at the same time is able to produce accurate spatial information, (2) it is possible to produce orthographic images of thermal infrared images, (3) the analysis of the temperature fluctuation characteristics of the solar panel and cell showed that the abnormal module and cell displayed a larger temperature change than the normal module and cell, and (4) the abnormal heat generation of the panel and cell can be accurately discerned by the abnormal state panel and cell through the spatial distribution of the temperature. It is concluded that the inspection method of the solar module using the obtained UAV-based thermal infrared sensor can be useful for safety inspection and monitoring of the rapidly growing solar power generation facility.

Normalized Difference Vegetation Index versus Dark Green Colour Index to estimate nitrogen status on bermudagrass hybrid and tall fescue

ABSTRACT In recent years digital sensors have been successfully integrated on board Unmanned Aerial Vehicles (UAV) to assess crop vigour, vegetation coverage, and to quantify the ‘greenness’ of foliage as indirect measurements of crop nitrogen status. The classical approach of precision agriculture has involved the use of multispectral sensors onboard UAV and the development of numerous vegetation indices associated with vegetation parameters, such as the mostly used Normalized Difference Vegetation Index (NDVI). However, the main negative issue when dealing with multi and hyper-spectral reflectance measuring tools is their high cost and complexity from the operational point of view. As a low-cost alternative, vegetation indices derived from Red Green Blue (RGB) cameras have been employed for remote-sensing assessment, providing data on different stress conditions and species. Digital images record information as amounts of RGB light emitted for each pixel of the image; however, the intensity of red and blue will often alter how green an image appears. To simplify the interpretation of digital colour data, recent studies have suggested converting RGB values to the more intuitive Hue, Saturation, and Brightness (HSB) colour spectrum, and then into a single measure of dark green colour, the Dark Green Color Index (DGCI). In this study, NDVI acquired by a ground-based handheld crop sensor and by a multispectral camera mounted on board a UAV has been compared with DGCI calculated from images taken with a commercial digital camera on board a UAV, trying to quantify the colour of turfgrass that had received different nitrogen (N) rates. The objectives of the trial were to study an affordable easy-to-use tool evaluating the relationship among NDVI, DGCI and leaf nitrogen content on turfgrass.

Atmospheric structures in the troposphere as revealed by high-resolution backscatter images from MU radar operating in range-imaging mode

VHF band stratosphere/troposphere (ST) radars around the globe are seldom operated in range-imaging mode. As such, the typical range resolution of their backscatter images is about 150 m. The only exception is the Kyoto University’s Middle and Upper Atmosphere (MU) radar in Shigaraki, Japan. Range imaging using frequency diversity was implemented there in 2005 and has often been used since then. During the Shigaraki UAV Radar Experiment (ShUREX) campaigns in the spring/summers of 2015, 2016, and 2017, the MU radar was operated in range-imaging mode to provide a range resolution of typically 20 m, for good signal to noise (SNR) ratios. The resulting Capon backscatter images revealed a variety of atmospheric structures in the moist troposphere in great detail. They were also quite useful in deploying in situ sensors on board unmanned aerial vehicles (UAVs) to probe such structures in near real time guided by the images. The goal of this paper is to present and discuss some such structures of interest to atmospheric dynamics collectively, to provide an overarching view. They include Kelvin-Helmholtz (KH) billows generated by shear instability, mid-level cloud-base turbulence (MCT) layers generated by convective instability in a moist troposphere, convective boundary layer (CBL), and sheet and layer (S&L) structures in a stably stratified atmospheric column. Videos of radar images collected during the 2015 and 2016 campaigns are included as Additional files 1, 2 and 3 with a brief explanatory text as Additional file 4 to demonstrate the fascinating, ever-changing evolution of atmospheric structures over the MU radar.