Spectral reflectance-based vicarious calibration (VicCal) requires accurate characterization of the bidirectional reflectance distribution function (BRDF) of the ground-based target. Railroad Valley ...(RRV) Playa, Nevada, has been used as a VicCal test site since 1995 as it is large, appears stable over time, and has a reasonably consistent surface. This study presents the results of a diurnal measurement cycle that closely replicated illumination geometries for Earth Observing (EO) satellites over a year. By measuring the rate of change of the BRDF with respect to time, we recorded the range of BRDF effects while holding the surface constant with respect to moisture and surface condition variation. The rate of spectral reflectance change increased rapidly with view angle in the backscatter direction, reaching rates of change that are 2.3 and 10.5 times greater in the backscatter than in the forward scatter direction for view angles of 20° and 40°, respectively. The results show that larger off-nadir viewing angles in the backscatter direction are particularly sensitive to changes in solar/view geometries.
The 41
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Canadian Symposium on Remote Sensing (CSRS) was a unique event, originally planned to be hosted as an in-person event in Yellowknife, Northwest Territories but ultimately delivered 100% ...online due to the COVID-19 global pandemic. As the 41
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CSRS represented an unprecedented departure from the CRSS-SCT's long history of annual in-person symposia, this note summarizes the transition from an in-person to an online event. In particular, delegate feedback on some of the challenges encountered, as well as positive and negative perceptions of the event delivery. It is important that a record of these collective experiences is preserved and considered for future symposia, and our experience is shared with the global research community.
Topographic correction based on sun-canopy-sensor (SCS) geometry is more appropriate than terrain-based corrections in forested areas since SCS preserves the geotropic nature of trees (vertical ...growth) regardless of terrain, view, and illumination angles. However, in some terrain orientations, SCS experiences an overcorrection problem similar to other simple photometric functions. To address this problem, we propose a new SCS+C correction that accounts for diffuse atmospheric irradiance based on the C-correction. A rigorous, comprehensive, and flexible method for independent validation based on canopy geometric optical reflectance models is also introduced as an improvement over previous validation approaches, and forms a secondary contribution of this paper. Results for a full range of slopes, aspects, and crown closures showed SCS+C provided improved corrections compared to the SCS and four other photometric approaches (cosine, C, Minnaert, statistical-empirical) for a Rocky Mountain forest setting in western Canada. It was concluded that SCS+C should be considered for topographic correction of remote sensing imagery in forested terrain.
The recent popularization of unmanned aerial vehicles (UAVs) for use in terrestrial remote-sensing science has brought a class of inexpensive and largely unmeasured set of sensors into the scientific ...domain. Remote-sensing science demands high-quality data for information production and requires that the radiometric and spectral characteristics of imaging systems are known. This study compared the radiometric and spectral characteristics of 10 imaging systems commonly used in UAV research. From very inexpensive board-level cameras, consumer-grade cameras and purpose built remote-sensing systems were tested. The results show that sensor non-linearity with respect to radiance is a major limitation in producing reliable results. Spectral results demonstrated a degree of similarity between sensors with broad overlapping spectral bands being the norm. Careful attention to radiometric correction and spectral characterization will enhance the quality of the data produced from these systems.
The foundation of all quantitative remote sensing is based on the ability of sensors to convert energy into digital signals. This process requires an understanding of the radiometric and spectral ...behaviour of the instrument. This information is rarely available for the consumer-grade digital cameras commonly used in unmanned aerial vehicle (UAV) systems. This study measured the spectral and radiometric characteristics of consumer-grade digital cameras in laboratory-based experiments. The spectral characteristics showed broad overlapping spectral bands in the visible and near-infrared wavelengths with spectral band widths between 70 and 100 nm. The radiometric response functions were non-linear in nature. The nonlinearity resulted in the inability of reliable spectral reflectance calculations. When compared to the spectral reflectance values computed from an ASD FieldSpec-3, differences were as high as 42% from the true value with average deviations between 23% and 32%. When characterized, the spectral reflectance values compared more favourably to ASD-computed spectral reflectance.
Relationships between vegetation indices (VIs) and leaf area index (LAI) tend to saturate in the nadir direction, and vary with crop canopy structure and view zenith angles (VZAs). The objective of ...this paper was to improve the monitoring accuracy and angular stability of VIs for estimating LAI using multiangular remote sensing data. The relationship between LAI and ground-based hyperspectral spectral reflectance was quantified in winter wheat (Triticum aestivum L.) exhibiting erectophile and planophile growth habits. To further reduce the saturation, species specificity, and angular sensitivity, we developed a saturation factor (SF), based on near-infrared and green bands. Multiplying all VIs by SF greatly improved the association with LAI across all VZAs (<inline-formula> <tex-math notation="LaTeX">R^{2} = 0.73{-}0.82 </tex-math></inline-formula>). Most VI <inline-formula> <tex-math notation="LaTeX">\times </tex-math></inline-formula> SF values, particularly optimized soil-adjusted VI <inline-formula> <tex-math notation="LaTeX">\times </tex-math></inline-formula> SF, were able to construct universal algorithms across VZAs for accurate estimation of LAI due to the sensitivity of SF to LAI in a dense canopy, and the insensitivity of SF to view effects with larger VZAs. This approach is also promising for the exploitation of multiangular satellite data for the design and calibration of nonview-angle-corrected spectral reflectance, for which the sensor is only deployed at fixed observation direction.
The landscape of post-secondary education has experienced a dramatic change in student outcomes over the past 20 years. The expectation for students in advanced education was a career in research and ...toward gaining employment in either academia or in government science. From our survey of university students and early career professionals, it was clear that there is an expectation gap between desired and probable post-secondary education outcomes. Our survey indicated that the majority of trainees, regardless of level of education, undervalue the importance of written and oral communication skills and overvalue specific methodological understanding relative to those employed in the field. While some of these dichotomies can be explained by the relative lack of experience of students, it also points to the nature of the foci of our training. While we are concerned with the production of the next leaders in remote sensing science, most will have careers that are different from their training. There is an opportunity to optimize the post-secondary education experience (student and faculty) with the inclusion of a broader view toward career outcomes.
The NS5A protein plays a critical role in the replication of HCV and has been the focus of numerous research efforts over the past few years. NS5A inhibitors have shown impressive in vitro potency ...profiles in HCV replicon assays, making them attractive components for inclusion in all oral combination regimens. Early work in the NS5A arena led to the discovery of our first clinical candidate, MK‐4882 2‐((S)‐pyrrolidin‐2‐yl)‐5‐(2‐(4‐(5‐((S)‐pyrrolidin‐2‐yl)‐1H‐imidazol‐2‐yl)phenyl)benzofuran‐5‐yl)‐1H‐imidazole. While preclinical proof‐of‐concept studies in HCV‐infected chimpanzees harboring chronic genotype 1 infections resulted in significant decreases in viral load after both single‐ and multiple‐dose treatments, viral breakthrough proved to be a concern, thus necessitating the development of compounds with increased potency against a number of genotypes and NS5A resistance mutations. Modification of the MK‐4882 core scaffold by introduction of a cyclic constraint afforded a series of tetracyclic inhibitors, which showed improved virologic profiles. Herein we describe the research efforts that led to the discovery of MK‐8742, a tetracyclic indole‐based NS5A inhibitor, which is currently in phase 2b clinical trials as part of an all‐oral, interferon‐free regimen for the treatment of HCV infection.
Effective treatment of chronic hepatitis C with direct‐acting antivirals will require combination therapy with multiple agents that target different steps in the viral replication cycle and impose a high barrier to resistance. MK‐8742 is a potent inhibitor of hepatitis C virus non‐structural protein 5A (HCV NS5A) that is being developed as a component of an once‐daily, all‐oral, interferon‐free regimen for the treatment of chronic HCV infection.
The derivation of the bidirectional reflectance distribution function (BRDF) from Earth surface features provides vital data for improved remote estimation of Earth surface features and properties. ...The angular component of a reflectance signature represents a valuable source of information that has largely been ignored due to the lack of empirical data. BRDF data products are now readily available from a variety of remote sensing platforms, and these require extensive field validation to ensure data quality and validity. This paper presents a high-performance, low-cost, and computer-controlled goniometer system capable of sampling surface BRDF and demonstrates several example applications. The system introduces a number of technological advances, including real-time reflectance calibration, programmable sampling schemes, zero target interference structure, and ease of portability. Using this instrument, BRDF estimates were gathered from a variety of agricultural crops in field and laboratory settings, with performance gains of four times the speed of current designs. This system can provide very fast acquisition of a BRDF estimate, depending on the desired angular resolution. Initial experiments demonstrate that this new style of hyperspectral goniometer is a significant advance over previous designs, with respect to scan capabilities, angular resolution, calibration, and portability.
Nitrogen (N) content is an important factor that can affect wheat production. The non-destructive testing of wheat canopy leaf N content through multi-angle hyperspectral remote sensing is of great ...importance for wheat production and management. Based on a 2-year experiment for winter wheat in Lethbridge (Canada), Zhengzhou (China), and Kaifeng (China) growing under different cultivation practices, the authors studied the relationships between N content and wheat canopy spectral data in solar principal plane (SPP) and perpendicular plane (PP) at different observation angles. Modeling was conducted according to the spectrum index with the highest correlation coefficient and the corresponding observation angle. The results showed that correlation coefficient between the spectral index and canopy leaf N content at each observation angle of the SPP was significantly higher than that of the PP. Significant differences in the correlation coefficient were also observed at different observation angles of the same observation plane, and the correlation coefficients of angles of −30° and −40° were higher than others. A model fitted by a power function by using mND705 as independent variable at an angle of −40° in the SPP showed the highest accuracy.
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