Digital terrain models (DTMs) present important data source for different applications in environmental disciplines including forestry. At regional level, DTMs are commonly created using airborne ...digital photogrammetry or airborne laser scanning (ALS) technology. This study aims to evaluate the vertical accuracy of DTMs of different spatial resolutions derived from high-density ALS data and existing photogrammetric (PHM) data in the dense lowland even-aged pedunculate oak forests located in the Pokupsko basin in Central Croatia. As expected, the assessment of DTMs' vertical accuracy using 22 ground checkpoints shows higher accuracy for ALS-derived than for PHM-derived DTMs. Concerning the different resolutions of ALS-derived (0.5 m, 1 m, 2 m, 5 m) and PHM-derived DTMs (0.5 m, 1 m, 2 m, 5 m, 8 m) compared in this research, the ALS-derived DTM with the finest resolution of 0.5 m shows the highest accuracy. The root mean square error (RMSE) and mean error (ME) values for ALS-derived DTMs range from 0.14 m to 0.15 m and from 0.09 to 0.12 m, respectively, and the values decrease with decreasing spatial resolution. For the PHM-derived DTMs, the RMSE and ME values are almost identical regardless of resolution and they are 0.35 m and 0.17 m, respectively. The findings suggest that the 8 m spatial resolution is optimal for a given photogrammetric data, and no finer than 8 m spatial resolution is required. This research also reveals that the national digital photogrammetric data in the study area contain certain errors (outliers) specific to the terrain type, which could considerably affect the DTM accuracy. Thus, preliminary evaluation of photogrammetric data should be done to eliminate possible outliers prior to the DTM generation in lowland forests with flat terrain. In the absence of ALS data, the finding in this research could be of interests to countries, which still rely on similar photogrammetric data for DTM generation. Keywords: DTM, ALS, LiDAR, stereo-photogrammetry, aerial images, even-aged forest stands, Central Croatia
Background and Purpose: Unmanned aerial vehicles (UAVs) are flexible to solve various surveying tasks which make them useful in many disciplines, including forestry. The main goal of this research is ...to evaluate the quality of photogrammetry-based digital surface model (DSM) from low-cost UAV’s images collected in non-optimal weather (windy and cloudy weather) and environmental (inaccessibility for regular spatial distribution of ground control points - GCPs) conditions.
Materials and Methods: The UAV-based DSMs without (DSMP) and with using GCPs (DSMP-GCP) were generated. The vertical agreement assessment of the UAV-based DSMs was conducted by comparing elevations of 60 checkpoints of a regular 100 m sampling grid obtained from LiDAR-based DSM (DSML) with the elevations of planimetrically corresponding points obtained from DSMP and DSMP-GCP. Due to the non-normal distribution of residuals (vertical differences between UAV- and LiDAR-based DSMs), a vertical agreement was assessed by using robust measures: median, normalised median absolute deviation (NMAD), 68.3% quantile and 95% quantile.
Results: As expected, DSMP-GCP shows higher accuracy, i.e. higher vertical agreement with DSML than DSMP. The median, NMAD, 68.3% quantile, 95% quantile and RMSE* (without outliers) values for DSMP are 2.23 m, 3.22 m, 4.34 m, 15.04 m and 5.10 m, respectively, whereas for DSMP-GCP amount to -1.33 m, 2.77 m, 0.11 m, 8.15 m and 3.54 m, respectively.
Conclusions: The obtained results confirmed great potential of images obtained by low-cost UAV for forestry applications, even if they are surveyed in non-optimal weather and environmental conditions. This could be of importance for cases when urgent UAV surveys are needed (e.g. detection and estimation of forest damage) which do not allow careful and longer survey planning. The vertical agreement assessment of UAV-based DSMs with LiDAR-based DSM confirmed the importance of GCPs for image orientation and DSM generation. Namely, a considerable improvement in vertical accuracy of UAV-based DSMs was observed when GCPs were used.
Background and Purpose:
Although organized forestry has existed in Croatia for more than 250 years, this mostly entailed state forests. During the last decade, Extension Services have started to ...support the development of forest management plans for privately owned forests. Lately, FMPs have been developed for nearly 3/4 of privately owned forests in Croatia. During the creation of those plans, yield tables and normal models for state-owned forests, primarily even-aged stands with long-time management, were used because similar data was not developed for uneven-aged and poorly managed forests. This research encompasses privately owned forests in the Croatian Mediterranean and sub-Mediterranean regions where holm oak (
Quercus ilex
L.) and downy oak (
Quercus pubescens
Willd.) are the prevailing species in forest stands. The main goal was to determine site indices revealed in the analysis of yearly radial increments and to create relevant yield tables.
Materials and Methods:
In this study, 1286 oak trees were cored to the centre on 377 locations spread in privately owned forests in Croatian Mediterranean and sub-Mediterranean regions. The ratio of trees and locations was approximately 3:1 for
Q. pubescens
. Some cored trees were more than two centuries old. After the standard sample preparation for dendrochronological analysis, cores were scanned, and tree-ring widths were determined. In total, ring width for over 67,000 rings was determined and measured.
Results:
Based on the data dispersion of cumulative tree increments at 40 years of age, 2 site index classes for
Q. ilex
and 3 for
Q. pubescens
were created based on k-means clustering. Prodan’s growth function was fitted to the created clusters to determine the site’s “model” tree. For the model trees, the percentage of volume growth was calculated. For easier field site index determination, height curves based on field data for each site index were calculated.
Conclusions:
For the first time in Croatia, systematic and controlled data on the growth (and age) of uneven-aged privately owned forests in the Croatian Mediterranean and sub-Mediterranean area were collected. Based on the data collected in the field, three different site indices for downy oak and two site indices for holm oak were determined. These results could find their application during operational forest management and forest exploitation because they allow for more accurate determination of the site production strength in the explored stands.
Privatne šume prema Šumskogospodarskoj osnovi RH 2006-2015 zauzimaju 22 % ukupne površine šuma i šumskog zemljišta u RH tj. oko 600.000 ha. Neke od značajki privatnih šuma su: da se radi o sitnim ...česticama i posjedima, na istoj površini nalazi se veći broj posjednika te iznimna nesređenost podataka u katastru. U ovom radu obrađeni su podaci o česticama i posjednicima iz 319 katastarskih općina (KO) raspoređenih u 5 regija Republike Hrvatske tj. u 53 gospodarske jedinice šuma šumoposjednika. Površinski uzorak predstavlja 8,74 % RH tj. prema ŠGO RH 15,69 % privatnih šuma RH. Osim prikaza sumarnih podataka po regijama, provedene su i dvije klaster analize radi dodatne karakterizacije regija. Prva klaster analiza se odnosi na varijable posjedništva: srednja površina čestica unutar KO obuhvaćenih programima gospodarenja šumama šumoposjednika (u daljem tekstu Programima), srednja površina posjeda unutar KO obuhvaćenim Programima te srednja količina posjednika na posjedovnim listovima unutar KO obuhvaćenim Programom. Druga klaster analiza se odnosi na varijable površina: ukupna površina KO, omjer zašumljenih površina šumama šumoposjednika pojedinačnih KO te omjer „nešumskog“ zemljišta prema katastarskom načinu uporabe obuhvaćenih Programima.
Ovo istraživanje dalo nam je uvid u najizraženiju značajku određene regije, kao i u jedinstvene odnose unutar promatranih značajki svake regije. Analizom je utvrđeno da se regije Istra i Kvarner, Slavonija te središnja Hrvatska više razlikuju od ostalih po vlasničkim varijablama, dok su regije Dalmacija te Gorski kotar i Lika bolje okarakterizirane prostornim varijablama. Također, kao rezultat klaster analiza potvrđeno je više zakonitosti vezanih za veličinu šumske čestice i količinu posjednika tj. za udio privatnih šuma u KO i udio „nešumskog“ zemljišta obuhvaćenim Programima.
Private owned forests occupy 22 % of the total forest and forest land area i.e. approximately 600,000 ha, according to Forest Management Plan for the area of the Republic of Croatia. Some of the private owned forest characteristics are as follows: small cadastral plots and estates, large number of landlords for the same area and great discrepancy of cadastral data. In this research, analyzed data about cadastral plots and landlords are taken from 319 cadastral municipalities (CM) distributed in 5 regions of the Republic of Croatia as well in 53 private owned forest management units. The sample represents 8.74 % of the Croatian area i.e. 15.69 % of the private owned forest area, according to the Forest Management Plan for the area of the Republic of Croatia. In addition to the statistical characteristic of the cadastral plots regarding regions, two cluster analyses are performed for better characterization of the regions. The first cluster analysis refers to the possession variables: average area of the cadastral plots inside CMs included in private-owned forest management plans (P-FMP), average area of the estates inside CMs included in P-FMP and average amount of the landlords in possession sheets by CMs included in P-FMP. Second cluster analysis refers to spatial variables: total area of the CMs, ratio of the forested areas by private-owned forests and ratio of the „non-forest” land according to cadastral land use data included in P-FMP.
This research gave us an insight about the most pronounced characteristic of each region and about unique relation of the observed characteristics for each region.
This research defines that regions Istria and Kvarner, Slavonija and central Croatia are more differentiated from the other regions in terms of possession variables, whilst the regions of Gorski kotar, Lika and Dalmatia are better explained with spatial variables as differentiation factor from other regions. Few principles are also confirmed as the results of the cluster analysis, for example the relation between the size of the cadastral plots and number of the landlords as well as relation regarding private owned forests ratio and ratio of the „non-forest“ land included in P-FMP.
Radi praćenja količine vezanog (tzv. priljeva) i emitiranog (tzv. odljeva) ugljika, kao i praćenja promjena, pozitivnih i negativnih, u veličini rezervoara (ponora) ugljika potrebno je razviti brze i ...jednostavne metode pomoću kojih se u vrlo kratkom roku mogu sakupiti velike količine podataka na velikom području, potrebnih za obračun ovih parametara. To se može postići implementirajući LIDAR tehnologiju za obračun nadzemne biomase vegetacije na velikim područjima i posljedično obračun vezanog ugljika odnosno ugljičnog dioksida, što u Republici Hrvatskoj predstavlja prvo istraživanje ovakvog tipa.
Jedan od ciljeva ovog istraživanja je izraditi model za utvrđivanje nadzemne biomase degradiranih šumskih područja u stadiju šikara (hipoteza 1), što je jedan od glavnih nedostajućih podataka pri određivanju količine vezanog ugljika i promjena u rezervoaru ugljika prilikom izrade Nacionalnog izviješća o stakleničkim plinovima.
Također će se utvrditi utjecaj manjih gustoća oblaka točaka na konačni rezultat (hipoteza 2). Korištenje nižih gustoća LIDAR oblaka radi dobivanja zadovoljavajućih i dovoljno preciznih podataka je direktno povezano s troškom snimanja koje predstavlja najveću stavku troška u ovakvim projektima.
Dio istraživanja je proveden u nizinskom području nadmorske visine približno 120 m, a drugi dio istraživanja je proveden u brežuljkastom području na nadmorskim visinama od približno 250 do 550 m. Terenskim prikupljanjem podataka (68 ploha), obradom LIDAR podataka (prosječne gustoće 1,38 točaka/m2) i na kraju regresijskim analizama izrađeni su regresijski modeli za procjenu biomase degradiranih šumskih područja nizinskog i brdskog vegetacijskog pojasa.
Utvrđeno je da je izrađeni model za nizinsko područje koeficijenta determinacije (R2) 0,75, dok je za brdsko područje 0,60. Također je utvrđeno da gustoća oblaka točaka nema utjecaja na prikladnost modela do određenih granica (do 0,4 točke/m2) čime su obje hipoteze uspješno potvrđene.
Primjenom izrađenih modela na cijelo područje, izračunate su vrijednosti šumske nadzemne biomase za cijelo istraživano područje. Isto tako, napravljena je usporedba prikladnosti izrađenih modela na osnovu rijeđih oblaka točaka za primjenu na cijelom području.
Na kraju ovog istraživanja, osim taksativno navedenih određenih praktičnih zaključaka i ograničenja pri samom istraživanju (vremenska nesukladnost LIDAR i terenskih podataka, nepostojanje lokalnih modela za procjenu biomase pojedinih stabala i sl.), navedene su i preporuke za daljnja istraživanja (prevladavanje postojećih ograničenja, ponavljanje ovog tipa istraživanja za biogeografska područja koja nisu obuhvaćena ovim istraživanjem i uvrštavanje dodatnih podloga i sl.).
In order to enable monitoring of the sequestered and emitted carbon quantities as well as changes, both positive and negative, in the carbon pool size (sink), it is necessary to develop fast and simple methods that can be used to collect large amounts of data on vast areas in order to calculate these parameters. The aforementioned can be achieved by implementing LIDAR technology for the calculation of above-ground biomass in vast areas and, consequently, for the calculation of sequestered carbon i.e. carbon dioxide, which is the first research of this kind in the Republic of Croatia.
One of the goals of this research is to create a model for determining above-ground biomass of degraded forest areas in thicket stadium (hypothesis 1), which is one of the main missing data for determining sequestered carbon quantities and changes in carbon sinks needed to create the Greenhouse Gasses National Inventory Report.
Also, the influence of thinner point cloud to the final result (in comparison to the initial one) shall be established (hypothesis 2). Lower density LIDAR cloud utilization with the aim of achieving satisfactory and precise enough data directly correlates to the costs of scanning that is the single highest cost in such projects.
A part of this research was conducted in the lowland area with altitude of approximately 120 m, whilst the other part of research was conducted in the hilly area with altitudes ranging from 250 to 550 m. Through field data collection (68 plots), processing of LIDAR data (average denstiy of 1.38 points/m2) and in the end regression analyses, regression models for the assessment of degraded forests biomass of lowland and hilly vegetation zone were developed.
It was determined that the model for the lowland area had determination coefficient (R2) of 0.75, whilst for hilly area this coefficient was 0.60. The results also show that cloud point density does not affect appropriateness of the model to a certain extent (up to 0.4 points/m2) which successfully confirms both hypotheses.
The application of created models to the entire area enabled calculation of forest above-ground biomass values for the whole researched area. Also, the comparison of appropriateness of thinner point cloud based models for the implementation on the entire area was conducted.
Finally, apart from the list of practical conclusions and limitations that have arisen during the research (time incompliance of LIDAR and field data, lack of local models for the assessment of above-ground tree biomass, etc.), recommendations for further researches are stated ie. overcoming existing restrictions, repeating this kind of the research for the bio-geographic areas that were not encompassed with this research and introduction of additional data.
Radi praćenja količine vezanog (tzv. priljeva) i emitiranog (tzv. odljeva) ugljika, kao i praćenja promjena, pozitivnih i negativnih, u veličini rezervoara (ponora) ugljika potrebno je razviti brze i jednostavne metode pomoću kojih se u vrlo kratkom roku mogu sakupiti velike količine podataka na velikom području, potrebnih za obračun ovih parametara. To se može postići implementirajući LIDAR tehnologiju za obračun nadzemne biomase vegetacije na velikim područjima i posljedično obračun vezanog ugljika odnosno ugljičnog dioksida, što u Republici Hrvatskoj predstavlja prvo istraživanje ovakvog tipa.
Jedan od ciljeva ovog istraživanja je izraditi model za utvrđivanje nadzemne biomase degradiranih šumskih područja u stadiju šikara (hipoteza 1), što je jedan od glavnih nedostajućih podataka pri određivanju količine vezanog ugljika i promjena u rezervoaru ugljika prilikom izrade Nacionalnog izviješća o stakleničkim plinovima.
Također će se utvrditi utjecaj manjih gustoća oblaka točaka na konačni rezultat (hipoteza 2). Korištenje nižih gustoća LIDAR oblaka radi dobivanja zadovoljavajućih i dovoljno preciznih podataka je direktno povezano s troškom snimanja koje predstavlja najveću stavku troška u ovakvim projektima.
Dio istraživanja je proveden u nizinskom području nadmorske visine približno 120 m, a drugi dio istraživanja je proveden u brežuljkastom području na nadmorskim visinama od približno 250 do 550 m. Terenskim prikupljanjem podataka (68 ploha), obradom LIDAR podataka (prosječne gustoće 1,38 točaka/m2) i na kraju regresijskim analizama izrađeni su regresijski modeli za procjenu biomase degradiranih šumskih područja nizinskog i brdskog vegetacijskog pojasa.
Utvrđeno je da je izrađeni model za nizinsko područje koeficijenta determinacije (R2) 0,75, dok je za brdsko područje 0,60. Također je utvrđeno da gustoća oblaka točaka nema utjecaja na prikladnost modela do određenih granica (do 0,4 točke/m2) čime su obje hipoteze uspješno potvrđene.
Primjenom izrađenih modela na cijelo područje, izračunate su vrijednosti šumske nadzemne biomase za cijelo istraživano područje. Isto tako, napravljena je usporedba prikladnosti izrađenih modela na osnovu rijeđih oblaka točaka za primjenu na cijelom području.
Na kraju ovog istraživanja, osim taksativno navedenih određenih praktičnih zaključaka i ograničenja pri samom istraživanju (vremenska nesukladnost LIDAR i terenskih podataka, nepostojanje lokalnih modela za procjenu biomase pojedinih stabala i sl.), navedene su i preporuke za daljnja istraživanja (prevladavanje postojećih ograničenja, ponavljanje ovog tipa istraživanja za biogeografska područja koja nisu obuhvaćena ovim istraživanjem i uvrštavanje dodatnih podloga i sl.).
Digital terrain models (DTMs) present important data source for different applications in environmental disciplines including forestry. At regional level, DTMs are commonly created using airborne ...digital photogrammetry or airborne laser scanning (ALS) technology. This study aims to evaluate the vertical accuracy of DTMs of different spatial resolutions derived from high-density ALS data and existing photogrammetric (PHM) data in the dense lowland even-aged pedunculate oak forests located in the Pokupsko basin in Central Croatia. As expected, the assessment of DTMs’ vertical accuracy using 22 ground checkpoints shows higher accuracy for ALS-derived than for PHM-derived DTMs. Concerning the different resolutions of ALS-derived (0.5 m, 1 m, 2 m, 5 m) and PHM-derived DTMs (0.5 m, 1 m, 2 m, 5 m, 8 m) compared in this research, the ALS-derived DTM with the finest resolution of 0.5 m shows the highest accuracy. The root mean square error (RMSE) and mean error (ME) values for ALS-derived DTMs range from 0.14 m to 0.15 m and from 0.09 to 0.12 m, respectively, and the values decrease with decreasing spatial resolution. For the PHM-derived DTMs, the RMSE and ME values are almost identical regardless of resolution and they are 0.35 m and 0.17 m, respectively. The findings suggest that the 8 m spatial resolution is optimal for a given photogrammetric data, and no finer than 8 m spatial resolution is required. This research also reveals that the national digital photogrammetric data in the study area contain certain errors (outliers) specific to the terrain type, which could considerably affect the DTM accuracy. Thus, preliminary evaluation of photogrammetric data should be done to eliminate possible outliers prior to the DTM generation in lowland forests with flat terrain. In the absence of ALS data, the finding in this research could be of interests to countries, which still rely on similar photogrammetric data for DTM generation.
U radu je na temelju podataka dobivenih laserskim skeniranjem iz zraka prikazana obrada 3D oblaka točaka te različiti načini i mogućnosti uporabe podataka pri praćenju i izmjeri vegetacije urbanih ...područja. U istraživanju su korišteni lidarski (engl. LiDAR = Light Detection and Ranging) podaci dobiveni u Zagrebu, točnije na Lenucijevoj potkovi, na Trgu Nikole Šubića Zrinskoga. Na istraživanom području za svako je locirano stablo određena vrsta i mjerena njegova visina (m) ultrazvučnim visinomjerom Vertex III. Terenskom izmjerom obuhvaćeno je 146 stabala (od toga 140 hibridnih platana (Platanus × hispanica) i 6 stabala javora mliječa (Acer platanoides L.). Prosječna izmjerena visina uređajem Vertex III iznosila je 24,0 m s rasponom od 5,60 m za najniže stablo do 36,0 m za najviše izmjereno stablo. Srednji prsni promjer iznosio je 74 cm s rasponom od 8 cm do 160 cm. Laserskim skeniranjem iz zraka i obradom prikupljenih podataka dobiven je georeferencirani 3D oblak točaka razvrstan u četiri razreda kao proizvod obrade sirovih podataka u softveru LAStools te prikazan u softveru QTM za vizualizaciju oblaka točaka. Prilikom očitavanja visine iz oblaka točaka izdvojena su 134 stabla. Srednja izmjerena visina stabala temeljem oblaka točaka iznosi 23,07 m, najniže izmjereno stablo visine je 5,31 m, a najviše 33,34 m. Statističkom obradom i usporedbom podataka dobiveni su koeficijent korelacije rs = 0,91 i koeficijent determinacije R2 = 0,83, dok je p = 0,000 (p < 0,05), što upućuje na statističku značajnost dobivene korelacije, a što potvrđuje validnost te upotrebljivost lidarskih podataka pri izmjeri i praćenju urbane vegetacije.
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