Multi-band Sensor Research Articles

UAS imaging-based decision tools for arid winter wheat and irrigated potato production management

ABSTRACTSmall unmanned aerial systems (UAS) are gaining global attention for rapid image-based decision making in agricultural production. In this study, the aim was to evaluate UAS-based imagery for rapid assessment of wheat winter survival and spring stand in winter wheat production and crop necrosis in potato production. Both are critical aspects of field (arid) and row (irrigated) crop farming practices. Aerial images from 97 hard and 352 soft single nucleotide polymorphism winter wheat plots, and 32 potato field plots (with 1 and 2 years of green manure applications) were acquired using a multi-band imaging sensor integrated with UAS. The UAS-based imagery was useful in evaluating winter wheat plant winter survival and spring stand, with Pearson correlation coefficient (r) in the range 0.60–0.82 between imagery and ground reference data. Similarly, the image-based potato field necrosis assessment showed a strong relationship with ground reference data (r = 0.93 and 0.88 for 1 and 2 years of green manure application, respectively). Overall, UAS imagery provided quantifiable, timely, and unbiased field data with high spatial resolution (about 2.3 cm/pixel for images acquired at 100 m altitude) that can aid in field and row crop production decision making.

Ultra-compact metamaterial absorber for multiband light absorption at mid-infrared frequencies

We investigated a multiband metamaterial absorber composed of one-side open cavities. A metallic sidewall effectively prevents destructive coupling between the neighboring cavities. Thus, the number of subunits in one period, which determines the number of multibands or the width of broadband, can be greatly increased. A redshift effect of the resonances is observed theoretically and numerically when the distance between the subunits is reduced. Although the separation is very small and the coupling between the neighboring cavities is strong, the angular insensitivity of the absorption is well-maintained over a wide range. Our findings may enable applications of ultra-compact multiband sensors and thermal emitters.

Multi-Band Terahertz Filter with Independence to Polarization and Insensitivity to Incidence Angles

Multi-band terahertz filters with independence to polarization and insensitivity to incidence angles are designed, fabricated, and measured, respectively. The promoted multi-band terahertz filters consist of two and three concentric ring complementary structure. Compared with the dual-ring structure, the triple-ring structure not only increases numbers of the pass bands but also heightens the out-of-band rejection of the middle band. The physical mechanisms of the multi-band resonant responses are clarified using three different configurations and distribution of magnetic fields and current surfaces. At normal incidence, the triple-ring structure is independent to polarization due to the symmetry. At oblique incidences, transmission magnitudes as a function of the frequency are firstly demonstrated for the multi-band filter; it is found that this structure shows great insensitivity to incidence angles. The multi-band filter also has advantages in easy fabrication. The encouraging results afforded by the design of the filters could find applications in multi-band sensors, terahertz communication systems, and other emerging terahertz technologies.

Fast colorization for single-band thermal video sequences

The color night-vision technology is advantageous to scene interpretation by displaying original monochrome night-vision imagery with colors, leading the future trend of night-vision development. Until recently, the methods of color night-vision are mostly based on multi-band sensor fusion that do not apply to thermal systems which are only sensitive to one spectral band. To address this, we present a novel technique in this paper aiming to directly give thermal videos day-time color appearance. We observe that the interframe pixel׳s luminance changing over thermal videos approximately follows a Double Lomax distribution. Based on this observation and computational reasons, we propose a star-shape mask for pixel matching. We further show how the mask can be used for efficient thermal video colorization. Additionally, considering the accumulating errors in sequence, we propose a simple region-similarity based abnormal color correction mechanism. Experiments on real applied thermal night-vision videos show that our method can efficiently render single-band thermal sequence with correct colors at 12–33 frame-per-second (fps), providing observers with enhanced facility of surrounding recognition and target recognition.

Development of multi‐band ultra‐high‐frequency sensor for partial discharge monitoring based on the meandering technique

To design high-sensitivity sensors is one of the critical issues to be solved for ultra-high-frequency (UHF) partial discharge (PD) detection in substations. Commonly-used UHF sensors usually use ultra-wideband antennas for the frequency bands ranging from 300 MHz to 1.5 GHz. To avoid interference in the frequency bands, such as signals generated from mobile phones, a new multi-band UHF sensor is proposed based on the loop antenna theory and meandering technique, which reduces the sensor size, provides high sensitivity and exhibits omnidirectional performance. The sensor works in the bandwidth ranges of 480–520, 800–850 and 1100–1200 MHz, and has sensitivity of more than 10 mm. The PD detection platform was set up, three typical insulation defects, such as corona discharge, surface discharge and free metal particle discharge, were designed, and then the tests were performed to compare the performance of the multi-band sensor and broadband sensor. The results show that the multi-band sensor's bandwidth covers the main spectra of PD signals, thereby can be used for detecting most kinds of PD signals. The sensor's sensitivity is higher than that of the broadband sensor with its size occupying only 5% of the latter, meeting the requirements for detection of PD sources in substations.

A Design of Multi-Band UHF Sensor for Partial Discharge Detection

The selection and design of the sensor is one of the key technologies for UHF PD detection. The UHF sensors popular used in PD detection and location in substation are partial discharge UHF sensor are usually ultra wideband antenna in the frequency range of 200 MHz to 1.5 GHz, which contains interference from communication signals. Accordingly, in order to improve the detection sensitivity and the signal-to-noise ratio, a kind of multi-band UHF narrowband sensor is proposed and designed in accordance with the principles of the loop antenna for PD detection. The proposed frequency resonant bands are set in the ranges of 480MHz-520MHz, 800MHz-850MHz and 1.1GHz-1.2GHz. The design based on simulation is finished and the performances of the prototype sensor are researched by parametric test and PD detection of three typical discharges: corona discharge, surface discharge and metallic particles discharge generated by PD mode. Results show that the selection of band for the UHF sensor is reasonable, and the sensor is with high sensitivity.

Optimal out-of-band correction for multispectral remote sensing

In this paper, an optimal out-of-band (OOB) correction transform (OOBCT) for dealing with onboard Visible/Infrared Imaging Radiometer Suite (VIIRS) OOB effects is proposed. This paper addresses the OOB response issue without consideration of the impact of other error sources on the correction processing. The OOBCT matrix is derived by minimizing an objective function of error summation between the expected and realistic recovered band-averaged spectral radiances. Using the VIIRS filter transmittance functions for all multiband sensors obtained from prelaunch laboratory measurements and a simulated dataset obtained from Airborne Visible InfraRed Imaging Spectrometer (AVIRIS) hyperspectral data, the OOBCT matrix is numerically computed. The processing of the OOB correction is straightforward and can be performed by a product between the OOBCT matrix and a measured multispectral image vector. The experimental results with both AVIRIS and Hyperspectral Imager for the Coastal Ocean datasets demonstrate that the ratios of average errors of recovered band-averaged spectral radiances divided by the measured radiances with the OOB responses are less than 4%. The average values of the relative errors for all pixels and bands indicate that the OOBCT method outperforms the works reported in literature.

Dynamic range and sensitivity requirements of satellite ocean color sensors: learning from the past

Sensor design and mission planning for satellite ocean color measurements requires careful consideration of the signal dynamic range and sensitivity (specifically here signal-to-noise ratio or SNR) so that small changes of ocean properties (e.g., surface chlorophyll-a concentrations or Chl) can be quantified while most measurements are not saturated. Past and current sensors used different signal levels, formats, and conventions to specify these critical parameters, making it difficult to make cross-sensor comparisons or to establish standards for future sensor design. The goal of this study is to quantify these parameters under uniform conditions for widely used past and current sensors in order to provide a reference for the design of future ocean color radiometers. Using measurements from the Moderate Resolution Imaging Spectroradiometer onboard the Aqua satellite (MODISA) under various solar zenith angles (SZAs), typical (L(typical)) and maximum (L(max)) at-sensor radiances from the visible to the shortwave IR were determined. The L(typical) values at an SZA of 45° were used as constraints to calculate SNRs of 10 multiband sensors at the same L(typical) radiance input and 2 hyperspectral sensors at a similar radiance input. The calculations were based on clear-water scenes with an objective method of selecting pixels with minimal cross-pixel variations to assure target homogeneity. Among the widely used ocean color sensors that have routine global coverage, MODISA ocean bands (1 km) showed 2-4 times higher SNRs than the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) (1 km) and comparable SNRs to the Medium Resolution Imaging Spectrometer (MERIS)-RR (reduced resolution, 1.2 km), leading to different levels of precision in the retrieved Chl data product. MERIS-FR (full resolution, 300 m) showed SNRs lower than MODISA and MERIS-RR with the gain in spatial resolution. SNRs of all MODISA ocean bands and SeaWiFS bands (except the SeaWiFS near-IR bands) exceeded those from prelaunch sensor specifications after adjusting the input radiance to L(typical). The tabulated L(typical), L(max), and SNRs of the various multiband and hyperspectral sensors under the same or similar radiance input provide references to compare sensor performance in product precision and to help design future missions such as the Geostationary Coastal and Air Pollution Events (GEO-CAPE) mission and the Pre-Aerosol-Clouds-Ecosystems (PACE) mission currently being planned by the U.S. National Aeronautics and Space Administration (NASA).

Multiband sensor using thick holographic gratings for sulfur detection by laser-induced breakdown spectroscopy

Detection of sulfur by optical emission spectroscopy generally presents some difficulties because the strongest lines are in the vacuum UV below 185 nm and therefore are readily absorbed by oxygen molecules in air. A novel concept for a low-cost and efficient system to detect sulfur using near-IR bands by laser-induced breakdown spectroscopy is here proposed. This concept is based on customized thick holographic gratings as spectral filtering elements. The signal integration and the temporal synchronization are performed using built-in custom electronics that amplify and integrate or trigger photodiode output signals. In this work, we use the near-IR lines at 921.287 nm and a background reference at 900 nm. Preliminary results show a limit of detection comparable to that of a conventional high-end system.

Multiband sensors for wireless electromagnetic field monitoring system - SEMONT

Substantial effort has been made to employ wireless sensor network and Internet technologies for environmental and habitat protection. Several monitoring systems are designed to collect data regarding temperature, humidity, pressure and some other environmental parameters, amongst which recently there is the exposure to electromagnetic field. In this paper, some basic features of the multiband sensors that are incorporated into the Serbian electromagnetic field monitoring network - SEMONT are presented. The SEMONT information network is designed and aimed for the remote, long-term, 24 hours a day, permanent broadband monitoring of the electromagnetic field in the environment.

Sensor Self-Localization for Antenna Arrays Subject to Bending and Vibrations

A method is presented for dealing with the array self-calibration problem with persistent and noncooperating narrowband sources such as TV, GSM, and radio emissions. We consider large and flexible antennas whose sensors are subject to important static distortions and dynamical vibrations. Such antennas can be found, for example, when a high-resolution array is inserted along the wings of an aircraft. We propose a self-calibration technique that solves phase ambiguities arising from the large static bending and estimates the current array shape. This two-step method can be used with a single carrier frequency or with multiband sensors. The performance of the method is evaluated with simulated data and is compared to the Cramer-Rao lower bound (CRLB).

A Multi-Band Dual-Polarized Antenna-Coupled TES Bolometer

We are developing multi-band dual-polarized antenna-coupled transition edge sensor (TES) bolometers for observing Cosmic Microwave Background (CMB) polarization anisotropies. We have designed a prototype pixel that uses a dual-polarized log-periodic antenna on a silicon hemispherical lens. Each polarization is coupled onto a separate microstrip transmission line. Microstrip filters are used to divide the broadband output of this antenna into a set of narrow frequency bands centered at 90, 150, and 220 GHz with bandwidths of 20%. We report on the fabrication of these devices as well as the initial optical testing.

Determination of Primary Spectral Bands for Remote Sensing of Aquatic Environments.

About 30 years ago, NASA launched the first ocean-color observing satellite:the Coastal Zone Color Scanner. CZCS had 5 bands in the visible-infrared domain with anobjective to detect changes of phytoplankton (measured by concentration of chlorophyll) inthe oceans. Twenty years later, for the same objective but with advanced technology, theSea-viewing Wide Field-of-view Sensor (SeaWiFS, 7 bands), the Moderate-ResolutionImaging Spectrometer (MODIS, 8 bands), and the Medium Resolution ImagingSpectrometer (MERIS, 12 bands) were launched. The selection of the number of bands andtheir positions was based on experimental and theoretical results achieved before thedesign of these satellite sensors. Recently, Lee and Carder (2002) demonstrated that foradequate derivation of major properties (phytoplankton biomass, colored dissolved organicmatter, suspended sediments, and bottom properties) in both oceanic and coastalenvironments from observation of water color, it is better for a sensor to have ~15 bands inthe 400 - 800 nm range. In that study, however, it did not provide detailed analysesregarding the spectral locations of the 15 bands. Here, from nearly 400 hyperspectral (~ 3-nm resolution) measurements of remote-sensing reflectance (a measure of water color)taken in both coastal and oceanic waters covering both optically deep and optically shallowwaters, first- and second-order derivatives were calculated after interpolating themeasurements to 1-nm resolution. From these derivatives, the frequency of zero values foreach wavelength was accounted for, and the distribution spectrum of such frequencies wasobtained. Furthermore, the wavelengths that have the highest appearance of zeros wereidentified. Because these spectral locations indicate extrema (a local maximum orminimum) of the reflectance spectrum or inflections of the spectral curvature, placing the bands of a sensor at these wavelengths maximizes the potential of capturing (and then restoring) the spectral curve, and thus maximizes the potential of accurately deriving properties of the water column and/or bottom of various aquatic environments with a multi-band sensor.

Information-theoretic assessment of sampled hyperspectral imagers

This work focuses on estimating the information conveyed to a user by hyperspectral image data. The goal is establishing the extent to which an increase in spectral resolution enhances the amount of usable information. Indeed, a tradeoff exists between spatial and spectral resolution due to physical constraints of multi-band sensors imaging with a prefixed SNR. After describing an original method developed for the automatic estimation of variance and correlation of the noise introduced by hyperspectral imagers, lossless interband data compression is exploited to measure the useful information content of hyperspectral data. In fact, the bit rate achieved by the reversible compression process takes into account both the contribution of the observation noise (i.e., information regarded as statistical uncertainty, but whose relevance to a user is null) and the intrinsic information of radiance sampled and digitized through an ideally noise-free process. An entropic model of the decorrelated image source is defined and, once the parameters of the noise, assumed to be Gaussian and stationary, have been measured, such a model is inverted to yield an estimate of the information content of the noise-free source from the code rate. Results are reported and discussed on both simulated and AVIRIS data.

Evaluation of multiband signal-to-clutter ratio as a performance metric for multispectral detection

There is currently great interest in determining optimal multiband sensor parameters for detection of tactical targets with known and unknown spectral signatures.1,2 Because many of the algorithms used to evaluate these parameters are iterative and computationally expensive, and generating receiver operating characteristics (ROC) curves requires that large amounts of data be processed at each parameter setting, it is desirable to have a quick and easy way to measure performance with a given set of parameters. The hope is that this performance metric will prove to have a direct relationship to ROC performance.

Multifrequency passive microwave remote sensing of soil moisture and roughness

Abstract The accuracy achievable in the surface soil moisture measurement of rough bare and vegetated soils, typical of the Italian landscape, has been investigated by using microwave experimental data collected by means of a multi-band sensor package (L, X, Ka and infrared bands). The thickness of soil that mainly affects the emission at the three microwave frequencies has been assessed. The sensitivity of L band emission to the moisture content of a soil layer about 5 cm thick has been confirmed, as well as the attenuation effect due to the surface roughness and presence of vegetation. A correction criterion based on the sensitivity to roughness and crop parameters of the highest frequencies (X and Ka bands) is proposed in order to increase the precision in soil moisture measurements.

Total reflected solar radiation calculated from multi-band sensor data

Reflected solar radiation is a significant term in the net radiation equation and is the one most strongly affected by surface conditions. The evaluation of net radiation over a heterogeneous area requires a detailed knowledge of the areal distribution of the reflected solar radiation. Remote sensing offers a means to obtain this areal distribution, provided that the total reflected solar spectrum can be estimated from discrete band multispectral radiometric data. A radiative transfer model was used to calculate the irradiance at the earth's surface for a number of atmospheric scattering and adsorption conditions. Response functions of two multiband radiometers were used to obtain the partial spectrum/total spectrum ( P/T) ratio for each radiometer at each atmospheric condition. It was found that the P/T ratio was essentially independent of atmospheric scattering and only mildly dependent on water vapor absorption. Reflectance spectral distributions for 14 different surface conditions (bare soil to full green canopy) were used along with the irradiance data to determine the P/T ratio for reflected solar radiation. Multispectral data, with the appropriate P/T ratio, were used to calculate the total incoming radiation and the total reflected radiation from a wheat canopy. The calculated data differed from wide band pyranometer data by about 5%. It was concluded that both total incoming and reflected solar radiation can be evaluated from multispectral radiometric data. This development is a step towards regional net radiation maps, and possibly regional evapotranspiration maps.

Some observations on the use of multiband spectral reconnaissance for the inventory of wildland resources

Three types of multiband sensors—multilens photographic systems, optical-mechanical scanners, and certain radar devices—are examined and their respective current capabilities to provide multiband data are reviewed. Information is presented, based on our research results and observations regarding these systems, which may help others to decide whether multiband spectral reconnaissance is, in part or wholly, the solution to their resource inventory problems.