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P4 Multispectral (P4M) camera setting for BRDF (bidirectional reflectance distribution function) measuring (VAA: vehicle azimuth angle, VZA: vehicle zenith angle, pitch interval: 10 • , and yaw interval: 15~30 • , Unit: • , ea).
Source publication
The bidirectional reflectance distribution function (BRDF) is important for estimating the physical properties of a surface in remote sensing. In the laboratory, the BRDF can be estimated quickly and accurately using a goniometer, but it is very difficult to operate in the field. The purpose of this study was to evaluate whether estimating the BRDF...
Contexts in source publication
Context 1
... flight height of the UAV goniometer was 6.8 m (VZA 70 • ) to 20 m (VZA 0 • (nadir)) from the ground, as shown in Figure 1b,c. The VZA and VAA interval for the BRDF and check flight is as shown in Table 1. The BRDF flight total images were 151 per band. ...Context 2
... flight height of the UAV goniometer was 6.8 m (VZA 70°) to 20 m (VZA 0°(nadir)) from the ground, as shown in Figure 1b,c. The VZA and VAA interval for the BRDF and check flight is as shown in Table 1. The BRDF flight total images were 151 per band. ...Context 3
... reflectance of each band was used for calibration and verification according to the manufacturer's recommendation equation and procedure [27]. Table 1. P4 Multispectral (P4M) camera setting for BRDF (bidirectional reflectance distribution function) measuring (VAA: vehicle azimuth angle, VZA: vehicle zenith angle, pitch interval: 10°, and yaw interval: 15~30°, Unit: °, ea.). ...Citations
... Goniometric determination of quantities like the total radiation emitted from a point like source from a UAV does benefit from a flight path that follows a spherical surface with constant distance to the source [1,2,3] instead of the usual flat mapping pattern with constant distance to the ground used [15]. Due to a limited accuracy of any positioning system and thus finite acceptance radius for waypoints they must not fall below a given minimal spacing. ...
Possible choices of flight paths on spherical surfaces-for example on hemispheres-for goniometric mapping with UAVs are compared and explicit parametrizations are given. The quantities measured during mapping should be easily integrable numerically in order to determine physical quantities like source strength, flux, etc. Some brief considerations regarding energy budget are given also.
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... Goniometric determination of quantities like the total radiation emitted from a point like source from a UAV does benefit from a flight path that follows a spherical surface with constant distance to the source [1,2,3] instead of the usual flat mapping pattern with constant distance to the ground used [15]. Due to a limited accuracy of any positioning system and thus finite acceptance radius for waypoints they must not fall below a given minimal spacing. ...
see https://www.techrxiv.org/
... There are BRDF models that can be applied to near-range remote sensing from UAVs, so called Kernel-driven models, such as the empirical Walthall model and the non-linear RPV model [16], which improve ARD products by correcting the reflectance in each band. In the last two years, several articles have been published addressing the BRDF effect from UAV imagery [17,18]. However, they do not rigorously consider the mathematical model of photogrammetry, the concealment effects based on the knowledge of the canopy geometry through the DSM, the elimination of areas in the images affected by the hotspot effect, and the consideration of optimal perspectives for removing the leaf pixels in which the vegetation cover is not directly exposed by the sun. ...
Close-range remote sensing techniques employing multispectral sensors on unoccupied aerial vehicles (UAVs) offer both advantages and drawbacks in comparison to traditional remote sensing using satellite-mounted sensors. Close-range remote sensing techniques have been increasingly used in the field of precision agriculture. Planning the flight, including optimal flight altitudes, can enhance both geometric and temporal resolution, facilitating on-demand flights and the selection
of the most suitable time of day for various applications. However, the main drawbacks stem from the lower quality of the sensors being used compared to satellites. Close-range sensors can capture spectral responses of plants from multiple viewpoints, mitigating satellite remote sensing challenges, such as atmospheric interference, while intensifying issues such as bidirectional reflectance distribution function (BRDF) effects due to diverse observation angles and morphological variances associated with flight altitude. This paper introduces a methodology for achieving high-quality vegetation indices under varied observation conditions, enhancing reflectance by selectively utilizing well-geometry vegetation pixels, while considering factors such as hotspot, occultation, and BRDF effects. A non-parametric ANOVA analysis demonstrates significant statistical differences between the proposed methodology and the commercial photogrammetric software AgiSoft Metashape, in a case study of a vineyard in Fuente-Alamo (Albacete, Spain). The BRDF model is expected to
substantially improve vegetation index calculations in comparison to the methodologies used in satellite remote sensing and those used in close-range remote sensing.
The Baotou sandy site in China is an important field site in the Committee on Earth Observation Satellites radiometric calibration network (RadCalNet), which freely releases the bottom-of-atmosphere (BOA) and top-of-atmosphere (TOA) spectral reflectance products in the spectral range from 400 nm to 1000 nm at 10 nm intervals with the aid of a set of automatic spectral and atmospheric parameter measurement devices. However, the released TOA and BOA spectral reflectance products are nadir-view spectral reflectance, which could produce errors if the Baotou sandy site is offset from the nadir point when they are utilized to calibrate one satellite sensor with the vicarious calibration method or to detect radiometric performance changes in the target sensor. Therefore, to address this problem and further broaden the applicable scopes of TOA spectral reflectance products, this article develops TOA and BOA bidirectional reflectance distribution function (BRDF) models using valid time-series TOA and BOA spectral reflectance products to fulfil BRDF correction. Then, the corrected TOA spectral reflectance is validated with the on-orbit measured TOA spectral reflectance of the Landsat8 Operational Land Imager (OLI) sensor with high and stable radiometric performance. After analysing the fitting accuracies of the BOA and TOA BRDF models, the influences of the filter criteria of valid time-series nadir-view BOA and TOA spectral reflectance, geo-positioning error of Landsat8/OLI, and aerosol type in the BOA BRDF correction process on the validation results are discussed. The results show that the BOA BRDF model obtains a better correction effect and is more stable than the TOA BRDF model.
