An Enhanced FGI-GSRx Software-Defined Receiver for the Execution of Long Datasets.

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).

Combating Single-Frequency Jamming through a Multi-Frequency, Multi-Constellation Software Receiver: A Case Study for Maritime Navigation in the Gulf of Finland.

Today, a substantial portion of global trade is carried by sea. Consequently, the reliance on Global Navigation Satellite System (GNSS)-based navigation in the oceans and inland waterways has been rapidly growing. GNSS is vulnerable to various radio frequency interference.

Potential of active multispectral lidar for detecting low reflectance targets.

The calibration and sampling of the multispectral Light Detection and Ranging (lidar) intensity is still challenging because the data acquisition has to be optimized for simultaneous 3D measurement, and the intensity retrieval methods need to be fast to enable real-time detection. We have studied the spectral measurement of low reflectance targets with an 8-channel hyperspectral lidar with improved waveform sampling and sensitivity, which now allow the detection of spectral differences even at low reflectance values. Our initial analysis resulted in a classification accuracy greater than 80%, which indicates that the multispectral lidar is able to detect the small differences in target spectral properties when reflectance at two or more channels is compared at the same time.

Improved waveform reconstruction and parameter accuracy retrieval for hyperspectral lidar data.

In this paper, we aim to provide a solution for choosing an optimized digitization frequency for full-waveform reconstruction of narrow FWHM laser pulses to improve the performance accuracy required for recognition and characterization of a wide range of materials with distinctive reflectance features. This type of analysis, for the first time, to the best of our knowledge, gives an assessment of the absolute accuracy with which waveform peak intensity and spatiotemporal peak location can be detected using multi- or hyperspectral lidar instrumentation. Different full-waveform reconstruction algorithms with varying characteristics are implemented on simulated Gaussian laser pulse data sets obtained with varying sampling frequencies ranging between 1 GHz and 5 GHz.

Portable hyperspectral lidar utilizing 5 GHz multichannel full waveform digitization.

The Finnish Geospatial Research Institute hyperspectral LiDAR (FGI HSL) was one of the first multichannel terrestrial LiDARs capable of producing simultaneous 3-dimensional topography with spectral data. Supercontinuum-based HSL instruments developed so far have suffered from portability and sensitivity issues, severely restricting potential applications. Recently, we have implemented a new robust field design of the FGI HSL together with an improved pulse digitizing scheme.

Uncertainty in multispectral lidar signals caused by incidence angle effects.

Multispectral terrestrial laser scanning (TLS) is an emerging technology. Several manufacturers already offer commercial dual or three wavelength airborne laser scanners, while multispectral TLS is still carried out mainly with research instruments. Many of these research efforts have focused on the study of vegetation.

Full waveform hyperspectral LiDAR for terrestrial laser scanning.

We present the design of a full waveform hyperspectral light detection and ranging (LiDAR) and the first demonstrations of its applications in remote sensing. The novel instrument produces a 3D point cloud with spectral backscattered reflectance data. This concept has a significant impact on remote sensing and other fields where target 3D detection and identification is crucial, such as civil engineering, cultural heritage, material processing, or geomorphological studies.

Absolute radiometric calibration of Als intensity data: effects on accuracy and target classification.

Radiometric calibration of airborne laser scanning (ALS) intensity data aims at retrieving a value related to the target scattering properties, which is independent on the instrument or flight parameters. The aim of a calibration procedure is also to be able to compare results from different flights and instruments, but practical applications are sparsely available, and the performance of calibration methods for this purpose needs to be further assessed. We have studied the radiometric calibration with data from three separate flights and two different instruments using external calibration targets.

Two-channel hyperspectral LiDAR with a supercontinuum laser source.

Recent advances in nonlinear fiber optics and compact pulsed lasers have resulted in creation of broadband directional light sources. These supercontinuum laser sources produce directional broadband light using cascaded nonlinear optical interactions in an optical fibre framework. This system is used to simultaneously measure distance and reflectance to demonstrate a technique capable of distinguishing between a vegetation target and inorganic material using the Normalized Difference Vegetation Index (NDVI) parameters, while the range can be obtained from the waveform of the echoes.

Use of naturally available reference targets to calibrate airborne laser scanning intensity data.

We have studied the possibility of calibrating airborne laser scanning (ALS) intensity data, using land targets typically available in urban areas. For this purpose, a test area around Espoonlahti Harbor, Espoo, Finland, for which a long time series of ALS campaigns is available, was selected. Different target samples (beach sand, concrete, asphalt, different types of gravel) were collected and measured in the laboratory.

Aperture size effects on backscatter intensity measurements in Earth and space remote sensing.

Most materials show a peaked intensity versus phase (light-source-target-detector angle) curve. For nonnegligible angular apertures of the source and/or the detector, the measured intensity at and near zero phase (backscatter) is lower than the real one. We derive an averaging aperture integral that represents this effect, and with it we invert measured intensity values to obtain the actual intensity curve.

Effect of incidence angle on laser scanner intensity and surface data.

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).

Backscattering measurements from individual Scots pine needles.

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.

Small-angle goniometry for backscattering measurements in the broadband spectrum.

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.

Laboratory experiments on backscattering from regolith samples.

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.