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We apply quantitative structure modelling to produce detailed information on branch-level metrics in trees. Particularly we are interested in the branch size distribution, by which we mean the total volume of branch parts distributed over the diameter classes of the parts. We investigate the possibility of predicting tree branch size distributions for trees in similar growing conditions. The quantitative structure model enables for the first time the comparisons of structure between a large number of trees. We found that the branch size distribution is similar for trees of different height in similar growing conditions. The results suggest that tree height could be used to estimate branch size distribution in areas with similar growing conditions and topography.

The Global Navigation Satellite System (GNSS) software-defined receivers offer greater flexibility, cost-effectiveness, customization, and integration capabilities compared to traditional hardware-based receivers, making them essential for a wide range of applications. The continuous evolution of GNSS research and the availability of new features require these software-defined receivers to upgrade continuously to facilitate the latest requirements. The Finnish Geospatial Research Institute (FGI) has been supporting the GNSS research community with its open-source implementations, such as a MATLAB-based GNSS software-defined receiver 'FGI-GSRx' and a Python-based implementation 'FGI-OSNMA' for utilizing Galileo's Open Service Navigation Message Authentication (OSNMA). In this context, longer datasets are crucial for GNSS software-defined receivers to support adaptation, optimization, and facilitate testing to investigate and develop future-proof receiver capabilities. In this paper, we present an updated version of FGI-GSRx, namely, FGI-GSRx-v2.0.0, which is also available as an open-source resource for the research community. FGI-GSRx-v2.0.0 offers improved performance as compared to its previous version, especially for the execution of long datasets. This is carried out by optimizing the receiver's functionality and offering a newly added parallel processing feature to ensure faster capabilities to process the raw GNSS data. This paper also presents an analysis of some key design aspects of previous and current versions of FGI-GSRx for a better insight into the receiver's functionalities. The results show that FGI-GSRx-v2.0.0 offers about a 40% run time execution improvement over FGI-GSRx-v1.0.0 in the case of the sequential processing mode and about a 59% improvement in the case of the parallel processing mode, with 17 GNSS satellites from GPS and Galileo. In addition, an attempt is made to execute v2.0.0 with MATLAB's own parallel computing toolbox. A detailed performance comparison reveals an improvement of about 43% in execution time over the v2.0.0 parallel processing mode for the same GNSS scenario. [ABSTRACT FROM AUTHOR]

We present a new approach for radiometric calibration of light detection and ranging (LIDAR) intensity data and demonstrate an application of this method to natural targets. The method is based on 1) using commercially available sand and gravel as reference targets and 2) the calibration of these reference targets in the laboratory conditions to know their backscatter properties. We have investigated the target properties crucial for accurate and consistent reflectance calibration and present a set of ideal targets easily available for calibration purposes. The first results from LIDAR-based brightness measurement of grass and sand show that the gravel-based calibration approach works in practice, is cost effective, and produces statistically meaningful results: Comparison of results from two separate airborne laser scanning campaigns shows that the relative calibration produces repeatable reflectance values. Index Terms--Calibration, laser measurements, laser radar, laser radiation effects, remote sensing.

We present a comprehensive experimental set of data on the dependence of the laser intensity on the angle of incidence to the target surface. The measurements have been performed in the laboratory for samples with a Nd:YAG laser and terrestrial laser scanner. The brightness scale data were also compared with data acquired by airborne laser scanning (ALS). The incidence angle effect is evident for all the targets. The effect is significant for incidence angles > 20[degrees], and stronger for bright targets. However, effects due to some of the other surface properties, such as roughness, were also detected. We also found a set of gravel samples for which the incidence angle effect was minor even up to 40[degrees]. The data provide an important reference for the interpretation and applications, e.g., full-waveform data processing of a laser scanner and ALS intensity calibration. OCIS codes: 280.3640, 280.1350, 290.5820.

Brightness measurement witb an airborne or terrestrial laser scanner is a new concept since the intensity information recorded by the laser scanner detectors has, thus far, not been used or implemented in surface brightness studies. This is partly due to the calibration problems and the lack of information on the behavior of laser light in the observation geometry where laser scanners operate. In addition, the 3-D position information has, thus far, been sufficient for surface modeling. We present a new type of empirical calibration scheme for laser scanner intensity developed with a terrestrial laser scanner in laboratory and field conditions using brightness targets and a calibrated reference panel. We compare the results with those obtained from airborne laser scanner flight campaigns using the same set of brightness targets. It turns out that the relative calibration of laser scanner intensity is possible using a calibrated grayscale but requires background information of the targets and the conditions in which the measurements are carried out. We also discuss the feasibility and uses of a laser-scanner-based intensity measurement in general. Index Terms--Backscatter, laboratory measurement, laser scanning, reflectance.

We present ground reference measurements of the directional scattering properties of conifer needles. As the development of multiangular remote sensing instruments sets a growing need for reliable ground reference measurement techniques and databases, there is an increasing demand for data on the spectral properties of conifer needles in forest reflectance modeling and the inversion of physically based models. These data are scarce due to technical and conceptual problems related to measuring thin needles, and the needle directional spectral properties are currently nonexistent even for single wavelengths. We present results from measuring the monochromatic backscattering of Scots pine needles in a controlled laboratory environment; we feel these results of the hot spot signatures of individual conifer needles are unique. The experiment was conducted at 1064 nm with an instrument constructed specifically for backscatter measurement, based on techniques commonly used for laser backscattering measurements and CCD photometry. Strong backscattering peaks near 0[degrees] were observed for the needles, the amplitude of the brightening being up to approximately 40%. OCIS codes: 290.1350, 140.3460.

The bidirectional reflection distribution functions (BRDF) of snow have been measured at high spectral resolution at various locations in Finland (Vuotso, Hyytiala, Sodankyla, Kilpisjarvi, Rovaniemi, Sodankyla again). The measured snow types include fresh, new snow, both needle-like and hexagonal flakes, old, loose snow, and melting and refrozen snow. All snow types show strong forward scattering as previously reported, but there also appeared to be some enhancement in the backward directions that has not been reported in much detail. The grain size gives a clear signal at near-infrared, which was observed previously. A nontrivial dependence on grain shape was also observed, which has been ignored previously. Melting snow has a distinct forward feature not observable in dry snow: first a maximum in specular direction, a minimum after that, and then again brightening forward. There is a spectral signal at 1250/1350 nm that could be useful for wetness recovery in particular, even when the topography or BRDF model is not known. Density dependence was observed, partially contradicting earlier measurements. Microtopographic roughness slightly increases backscattering as expected. Much more detailed information about snow could be observed using hyperspectral, multidirectional remote sensing techniques than with current instruments. Measurements of more snow types need to be taken, especially dirty snow, snow/vegetation composites, and rough snow surfaces. Index Terms--Bidirectional reflection distribution functions (BRDF), goniometer, hyperspectral, measurement, multidirectional, reflection, remote sensing, scattering, snow, spectrometer.

We present experiments on spectral bidirectional reflectance distribution function (BRDF) effects at backscatter and discuss the feasibility of new methods for laboratory and field simulations of remote sensing of land surfaces. The extreme sharpness of the intensity peak allows both directional and comparative experimental spectral studies of hot spots. We demonstrate wavelength-dependent features in the hot-spot reflectance signatures that facilitate extension of spectral and directional BRDF measurements of natural targets (such as forest understories and ice surfaces) into retroreflection to exploit their hot-spot characteristics in the interpretation of spaceborne and airborne data. OCIS codes: 290.1350, 290.5820, 280.0280.

We present new observations and models of the shapes and rotational states of the eight near-Earth Asteroids (1580) Betulia, (1627) Ivar, (1980) Tezcatlipoca, (2100) Ra-Shalom, (3199) Nefertiti, (3908) Nyx, (4957) Brucemurray, and (5587) 1990 SB. We also outline some of their solar phase curves, corrected to common reference geometry with the models. Some of the targets may feature sizable global nonconvexities, but the observable solar phase angles were not sufficie ntly high for confirming these. None is likely to have a very densely cratered surface. We discuss the role of the intermediate topographic scale range in photometry, and surmise that this scale range is less important than large or small scale lengths. Keywords: Asteroids, rotation; Photometry: Surfaces, asteroids

The investigation of the backscattering peak has applications in the surface texture characterization of asteroids and planetary surfaces. Laboratory experiments are important because they give an opportunity for systematic variation and comparison of samples. A backscattering experiment from regolith samples, which uses a laser light source and a beam splitter to reach the smallest phase angles, is presented. Measurements at zero and small phase angles for Sahara sand and meteorite rocks are made, and the preliminary results are presented in comparison with the phase curve observed for asteroid 69 Hesperia. The results are applicable to the further interpretation of the coherent backscattering opposition effect. OCIS codes: 290.1350, 290.5820, 120.5240.