Joel P. Younger

Accurate estimation of forest structural attributes over operational scales remains challenging because unmanned laser scanning (ULS) provides extensive spatial coverage but limited representation of internal stem structure, whereas terrestrial and mobile laser scanning (TLS/MLS) provide detailed stem measurements over relatively small areas. This study investigates a calibration-transfer framework in which small areas of terrestrial or fused LiDAR are used to improve diameter at breast height (DBH) estimation across much larger regions surveyed only by ULS. ULS, TLS, MLS and fused laser scanning (FLS) datasets were analysed for radiata pine and eucalyptus plantations. TreeLS-derived DBH measurements from terrestrial and fused point clouds were used as reference data to evaluate several distribution-aware and voxel-based imputation approaches for correcting regression-derived ULS estimates. Across the study sites, the best-performing imputation methods reduced stand-level mean DBH differences by as much as 95% relative to the uncorrected ULS regression estimates, resulting in substantially improved agreement with field-observed stand means while simultaneously producing DBH distributions that more closely matched the corresponding TreeLS-derived reference distributions. Voxel-based imputation performed particularly well for radiata pine and remained competitive for eucalyptus, while several distribution-based approaches achieved comparable or better performance in particular stands. These findings demonstrate the potential for transferring information from relatively small terrestrial LiDAR calibration areas to larger ULS-only acquisitions, improving stand-level DBH distribution estimates without requiring complete terrestrial coverage. Because validation was performed using stand-level field summary statistics rather than matched individual trees, the reported performance should be interpreted as demonstrating the potential of the approach under the conditions evaluated rather than universal individual-tree accuracy.

Forest inventory operations require accurate and scalable methods for estimating structural tree attributes such as diameter at breast height, tree height, and crown dimensions. Terrestrial laser scanning (TLS) and mobile laser scanning (MLS) provide detailed stem information but limited spatial coverage, whereas unmanned laser scanning (ULS) provides broad coverage but sparse internal stem structure. This study evaluates whether fused LiDAR point clouds and imputation-based correction methods can transfer accurate stem information from TLS, MLS, or fused calibration areas to larger ULS-only areas. ULS, TLS, MLS, and fused laser scanning (FLS) were analysed for 10 m and 20 m radiata pine, and 30 m eucalyptus stands. The TreeLS R package and regression-based methods were used for attribute extraction, and several imputation strategies were tested, including parametric cumulative distribution function (CDF) mapping, empirical and rank-based quantile mapping, conditional mean with residual spread restoration, and voxel-based imputation. The results show that TreeLS applied to TLS, MLS, and FLS produced substantially more reliable diameter at breast height (DBH) distributions than regression models applied directly to ULS data. For ULS-only areas, uncorrected regression estimates differed from field means by 2.0 cm for tall radiata pine, 10.4 cm for medium radiata pine, and 5.4 cm for mature eucalyptus. Using terrestrially trained voxel-based imputation reduced these differences to 0.1 cm, 0.3 cm, and 0.8 cm, respectively. Other distribution-aware imputation methods also substantially improved agreement with field-observed DBH distributions. These findings indicate that relatively small areas of high-density TLS or MLS or FLS data can be used to calibrate inventory estimates across larger ULS-only regions. The approach offers a practical compromise between the structural accuracy of terrestrial LiDAR and the spatial efficiency of aerial LiDAR, supporting scalable forest inventory estimation without requiring exhaustive terrestrial coverage.

Observations of neutral density in the mesosphere and lower thermosphere (MLT) region of the terrestrial atmosphere are important for understanding lower atmospheric, geomagnetic, and anthropogenic forcing. This study introduces a statistical method for measuring neutral density variations using an extensive dataset of meteor head echoes that were observed using the MAARSY high-power large-aperture (HPLA) mesosphere–stratosphere–troposphere (MST) radar. The method relies on observing the mean geocentric velocity of meteor head echoes as a function of initial detection altitude and day-of-year. The meteor head echo catalog used contains 1.4 million meteor head echoes between 2016–2023. Neutral density variations are observed with a 3 day time and 2 km altitude resolution between 85–115 km. The measurements show variations in neutral density potentially due to geomagnetic and atmospheric events. Variations of 20–40 % are common in the dataset, and agree with the magnitude of atmospheric neutral density fluctuations from an Upper-Atmosphere ICOsahedral Non-hydrostatic (UA-ICON) atmosphere model run.

A 31 MHz meteor radar located in Svalbard has been used to observe polar mesospheric echoes (PMSE) during summer 2020. Data from 19 July was selected for detailed analysis, with a focus on extracting additional information to characterize the atmosphere in the PMSE region. The use of an all-sky meteor radar adds an additional use to data collected for meteor observations and enables the detection of PMSE layers across a wide field of view. Comparison with data from a 53.5 MHz narrow-beam MST radar shows good agreement in the morphology of the layer as detected between the two systems. Doppler spectra of PMSE layers reveal fine structure, including regions of enhanced return that move across the radar's field of view. The relationship between range and Doppler shift of off-zenith portions of the layer enable the estimation of wind speeds with high temporal resolution during PMSE conditions. Trials demonstrate good agreement between wind speeds obtained from PMSE Doppler spectra and those calculated from specular meteor trail radial velocities. Combined with the antenna polar diagram of the radar, this same relationship was used to infer the aspect sensitivity of observed PMSE backscatter, yielding a mean backscatter angular width of 6.6 ± 2.8°. A comparison of underdense meteor radar echo decay times during and outside of PMSE conditions did not demonstrate a strong correlation between the presence of PMSE and shortened underdense meteor radar echo durations.

A 31 MHz meteor radar located in Svalbard has been used to observe polar mesospheric echoes (PMSE) during summer 2020. Data from 19 July was selected for detailed analysis, with a focus on extracting additional information to characterize the atmosphere in the PMSE region. The use of an all-sky meteor radar adds an additional use to data collected for meteor observations and enables the detection of PMSE layers across a wide field of view. Comparison with data from a 53.5 MHz narrow-beam MST radar shows good agreement in the morphology of the layer as detected between the two systems. Doppler spectra of PMSE layers reveal fine structure, including regions of enhanced return that move across the radar's field of view. The relationship between range and Doppler shift of off-zenith portions of the layer enable the estimation of wind speeds with high temporal resolution during PMSE conditions. Trials demonstrate good agreement between wind speeds obtained from PMSE Doppler spectra and those calculated from specular meteor trail radial velocities. Combined with the antenna polar diagram of the radar, this same relationship was used to infer the aspect sensitivity of observed PMSE backscatter, yielding a mean backscatter angular width of 6.6 ± 2.8°. A comparison of underdense meteor radar echo decay times during and outside of PMSE conditions did not demonstrate a strong correlation between the presence of PMSE and shortened underdense meteor radar echo durations.

A 31 MHz meteor radar located in Svalbard has been used to observe polar mesospheric echoes (PMSE) during summer 2020. Data from 19 July was selected for detailed analysis, with a focus on extracting additional information to characterize the atmosphere in the PMSE region. The use of an all-sky meteor radar adds an additional use to data collected for meteor observations and enables the detection of PMSE layers across a wide field of view. Comparison with data from a 53.5 MHz narrow-beam MST radar shows good agreement in the morphology of the layer as detected between the two systems. Doppler spectra of PMSE layers reveal fine structure, including regions of enhanced return that move across the radar's field of view. The relationship between range and Doppler shift of off-zenith portions of the layer enable the estimation of wind speeds with high temporal resolution during PMSE conditions. Trials demonstrate good agreement between wind speeds obtained from PMSE Doppler spectra and those calculated from specular meteor trail radial velocities. Combined with the antenna polar diagram of the radar, this same relationship was used to infer the aspect sensitivity of observed PMSE backscatter, yielding a mean backscatter angular width of 6.6 ± 2.8°. A comparison of underdense meteor radar echo decay times during and outside of PMSE conditions did not demonstrate a strong correlation between the presence of PMSE and shortened underdense meteor radar echo durations.

A 31 MHz meteor radar located in Svalbard has been used to observe polar mesospheric echoes (PMSE) during summer 2020. Data from 19 July was selected for detailed analysis, with a focus on extracting additional information to characterize the atmosphere in the PMSE region. The use of an all-sky meteor radar adds an additional use to data collected for meteor observations and enables the detection of PMSE layers across a wide field of view. Comparison with data from a 53.5 MHz narrow-beam MST radar shows good agreement in the morphology of the layer as detected between the two systems. Doppler spectra of PMSE layers reveal fine structure, including regions of enhanced return that move across the radar's field of view. The relationship between range and Doppler shift of off-zenith portions of the layer enable the estimation of wind speeds with high temporal resolution during PMSE conditions. Trials demonstrate good agreement between wind speeds obtained from PMSE Doppler spectra and those calculated from specular meteor trail radial velocities. Combined with the antenna polar diagram of the radar, this same relationship was used to infer the aspect sensitivity of observed PMSE backscatter, yielding a mean backscatter angular width of 6.6 ± 2.8°. A comparison of underdense meteor radar echo decay times during and outside of PMSE conditions did not demonstrate a strong correlation between the presence of PMSE and shortened underdense meteor radar echo durations.

A 31 MHz meteor radar located in Svalbard has been used to observe polar mesospheric echoes (PMSE) during summer 2020. Data from 19 July was selected for detailed analysis, with a focus on extracting additional information to characterize the atmosphere in the PMSE region. The use of an all-sky meteor radar adds an additional use to data collected for meteor observations and enables the detection of PMSE layers across a wide field of view. Comparison with data from a 53.5 MHz narrow-beam MST radar shows good agreement in the morphology of the layer as detected between the two systems. Doppler spectra of PMSE layers reveal fine structure, including regions of enhanced return that move across the radar's field of view. The relationship between range and Doppler shift of off-zenith portions of the layer enable the estimation of wind speeds with high temporal resolution during PMSE conditions. Trials demonstrate good agreement between wind speeds obtained from PMSE Doppler spectra and those calculated from specular meteor trail radial velocities. Combined with the antenna polar diagram of the radar, this same relationship was used to infer the aspect sensitivity of observed PMSE backscatter, yielding a mean backscatter angular width of 6.6 ± 2.8°. A comparison of underdense meteor radar echo decay times during and outside of PMSE conditions did not demonstrate a strong correlation between the presence of PMSE and shortened underdense meteor radar echo durations.