Point accuracy of combined pseudorange and carrier phase differential GPS under forest canopy

1999 ◽  
Vol 29 (5) ◽  
pp. 547-553 ◽  
Author(s):  
Erik Næsset
Keyword(s):  
Carrier Phase ◽  
Forest Canopy ◽  
Basal Area ◽  
Single Frequency ◽  
Deciduous Tree ◽  
Differential Gps ◽  
Positional Accuracy ◽  
Combined Use ◽  
Tree Canopies ◽  
The Mean

One 6-channel and two 12-channel single frequency GPS receivers observing C/A (course/acquisition) code and carrier phase were tested to determine positional point accuracies under conifer and deciduous tree canopies. Positional accuracies were determined for 38 subcanopy sites by differential processing of C/A code observations only and combined use of C/A code and carrier phase. Observation periods of 2.5-30 min were evaluated. Mean positional accuracy ranged from 1.17 to 3.70 m for the 12-channel receivers based on 2.5-30 min of observation of C/A code. Mean accuracy ranged from 0.79 to 2.25 m for combined use of C/A code and carrier phase. The accuracy was 7.34 m with 30 min of C/A code observations with the 6-channel receiver. With combined use of C/A code and carrier phase the mean accuracy of the 6-channel receiver increased to 0.98-2.44 m. The accuracy increased with decreasing basal area and improving geometric satellite distribution. The mean accuracy was significantly higher for the 12-channel receivers than for the 6-channel receiver and significantly higher by combined use of C/A code and carrier phase than use of C/A code only.

Potential of UltraCamX stereo images for estimating timber volume and basal area at the plot level in mixed European forests

2013 ◽  
Vol 43 (8) ◽  
pp. 731-741 ◽  
Author(s):  
Christoph Straub ◽  
Christoph Stepper ◽  
Rudolf Seitz ◽  
Lars T. Waser
Keyword(s):  
Point Cloud ◽  
Forest Canopy ◽  
Complex Structure ◽  
Mixed Forest ◽  
Basal Area ◽  
Deciduous Tree ◽  
Stereo Images ◽  
Timber Volume ◽  
European Forests ◽  
Forest Attributes

Current technical advances in the field of digital photogrammetry demonstrate the great potential of automatic image matching for deriving dense surface measurements of the forest canopy. In contrast to airborne laser scanning (ALS), aerial stereo images are updated more regularly by national or regional mapping agencies in several countries. Frequently, ALS-based terrain models (DTMs) are available, and thus photogrammetric canopy heights can be derived. However, currently, there is little knowledge as to how accurately forest attributes can be modeled using the aerial stereo images acquired by these official, regular aerial surveys, especially for mixed forests in central Europe. Thus, a photogrammetric point cloud derived from UltraCamX stereo images in combination with an ALS-DTM and a classification of coniferous and deciduous tree regions (based on orthoimages) was used to create a stratified estimation of timber volume and basal area in a mixed forest in Germany. Suitable models were derived at the plot level using explanatory variables from the photogrammetric point cloud (which was normalized using an ALS-DTM). The prior stratification of conifer- and deciduous-dominated field plots slightly improved the estimation accuracy. The results verify that stereo images can be an alternative to ALS data for modeling key forest attributes, even in mixed central European forests with complex structure.

A New Method For DGPS Ambiguity Resolution

2010 ◽  
Vol 63 (4) ◽  
pp. 645-661 ◽  
Author(s):  
Fabrizio Pieregentili ◽  
Emiliano Cordelli
Keyword(s):  
Ambiguity Resolution ◽  
Carrier Phase ◽  
Single Frequency ◽  
Double Difference ◽  
Phase Ambiguity ◽  
Differential Gps ◽  
Basic Principles ◽  
Baseline Vector ◽  
Phase Ambiguity Resolution ◽  
Carrier Phase Ambiguity

This paper deals with the problem of determining the baseline vector between two GPS receivers in single frequency (L1) using the basic principles of interferometric Differential GPS, therefore using the interferometric relations between the two receivers and the satellites visible to both receivers. As a preliminary step, ambiguity identification was solved using the results provided by the Kalman filter; these results were optimized by evaluating the Dilution Of Precision indexes for satellites in view of the receivers. Results achieved by applying this first procedure to data collected are discussed. To increase the accuracy of the results, a new, computationally fast algorithm for carrier phase ambiguity resolution on data collected from static and dynamics acquisitions was developed, implemented and tested. The new algorithm permitted an increase of accuracy of about two orders of magnitude with respect to results given by filtered Double Difference in the resolution of baseline vector.

Effects of Multiple Photon Scattering in Deciduous Tree Canopies

2009 ◽  
Author(s):  
Michael Greiner ◽  
Bradley D. Duncan ◽  
Matthew P. Dierking
Keyword(s):  
Deciduous Tree ◽  
Photon Scattering ◽  
Tree Canopies

scholarly journals Improving DGNSS Performance through the Use of Network RTK Corrections

2021 ◽  
Vol 13 (9) ◽  
pp. 1621
Author(s):  
Duojie Weng ◽  
Shengyue Ji ◽  
Yangwei Lu ◽  
Wu Chen ◽  
Zhihua Li
Keyword(s):  
Carrier Phase ◽  
Local Area ◽  
Satellite System ◽  
High Accuracy ◽  
Single Frequency ◽  
Baseline Length ◽  
Low Latitude ◽  
Phase Measurements ◽  
Network Rtk ◽  
Global Navigation Satellite

The differential global navigation satellite system (DGNSS) is an enhancement system that is widely used to improve the accuracy of single-frequency receivers. However, distance-dependent errors are not considered in conventional DGNSS, and DGNSS accuracy decreases when baseline length increases. In network real-time kinematic (RTK) positioning, distance-dependent errors are accurately modelled to enable ambiguity resolution on the user side, and standard Radio Technical Commission for Maritime Services (RTCM) formats have also been developed to describe the spatial characteristics of distance-dependent errors. However, the network RTK service was mainly developed for carrier-phase measurements on professional user receivers. The purpose of this study was to modify the local-area DGNSS through the use of network RTK corrections. Distance-dependent errors can be reduced, and accuracy for a longer baseline length can be improved. The results in the low-latitude areas showed that the accuracy of the modified DGNSS could be improved by more than 50% for a 17.9 km baseline during solar active years. The method in this paper extends the use of available network RTK corrections with high accuracy to normal local-area DGNSS applications.

Biomass estimates derived from sector subsampling of 360° spherical images

2021 ◽  
Author(s):  
Xiao Dai ◽  
Mark J Ducey ◽  
Haozhou Wang ◽  
Ting-Ru Yang ◽  
Yung-Han Hsu ◽  
...  
Keyword(s):  
Basal Area ◽  
Sampling Errors ◽  
Eastern Canada ◽  
Individual Tree ◽  
Inventory Costs ◽  
Standard Error Estimation ◽  
The Mean ◽  
Biomass Ratio ◽  
Spherical Images ◽  
Additional Level

Abstract Efficient subsampling designs reduce forest inventory costs by focusing sampling efforts on more variable forest attributes. Sector subsampling is an efficient and accurate alternative to big basal area factor (big BAF) sampling to estimate the mean basal area to biomass ratio. In this study, we apply sector subsampling of spherical images to estimate aboveground biomass and compare our image-based estimates with field data collected from three early spacing trials on western Newfoundland Island in eastern Canada. The results show that sector subsampling of spherical images produced increased sampling errors of 0.3–3.4 per cent with only about 60 trees measured across 30 spherical images compared with about 4000 trees measured in the field. Photo-derived basal area was underestimated because of occluded trees; however, we implemented an additional level of subsampling, collecting field-based basal area counts, to correct for bias due to occluded trees. We applied Bruce’s formula for standard error estimation to our three-level hierarchical subsampling scheme and showed that Bruce’s formula is generalizable to any dimension of hierarchical subsampling. Spherical images are easily and quickly captured in the field using a consumer-grade 360° camera and sector subsampling, including all individual tree measurements, were obtained using a custom-developed python software package. The system is an efficient and accurate photo-based alternative to field-based big BAF subsampling.

Carbon Stocks of Linear Category of Trees Out Side Forest in Anantapuramu District, Andhra Pradesh, India

2016 ◽  
Vol 39 (4) ◽  
pp. 303-308
Author(s):  
G. Kavitha ◽  
S. Salamma ◽  
M. Ramesh ◽  
Mudavath Naik ◽  
M. Kumar ◽  
...  
Keyword(s):  
Basal Area ◽  
Carbon Stocks ◽  
Linear Structures ◽  
Carbon Sequestration Potential ◽  
Sequestration Potential ◽  
The Mean ◽  
Angiosperm Species ◽  
Linear Category ◽  
Total Tree ◽  
Trees Outside Forest

In the present study, carbon stocks of linear structures of trees outside forest in Anantapuramu district was estimated through sampling of 344 (0.1 ha) plots. A total of 4229 tree individuals belonging to 66 angiosperm species were enumerated in the sampled plots. The mean tree density is 122.8per ha; mean diameter at breast height 4.04 m; mean basal area 15.43 m2 ha-1.Mean volume of trees with >10 cm diameter is 15.50 m3 ha-1; mean total tree biomass is 120.81 tons ha-1.The mean carbon stock is 57.385 tons ha-1 and extrapolated biomass and carbon content for linear structures are 0.176 Mt and 0.083 Mt respectively. The carbon sequestration potential of trees outside forests of Anantapuramu district is estimated at 0.304 Mt.

Factors affecting interannual variation in growth of western Canadian aspen forests during 1951-2000

2005 ◽  
Vol 35 (3) ◽  
pp. 610-622 ◽  
Author(s):  
EH (Ted) Hogg ◽  
James P Brandt ◽  
B Kochtubajda
Keyword(s):  
Populus Tremuloides ◽  
Interannual Variation ◽  
Regional Scale ◽  
Forest Health ◽  
Basal Area ◽  
Deciduous Tree ◽  
Severe Drought ◽  
Moisture Index ◽  
Canadian Prairies ◽  
The North

Trembling aspen (Populus tremuloides Michx.) is the most important deciduous tree in the North American boreal forest and is also the dominant tree in the aspen parkland zone along the northern edge of the Canadian prairies. Since the 1990s, observations of dieback and reduced growth of aspen forests have led to concerns about the potential impacts of climate change. To address these concerns, a regional-scale study (CIPHA) was established in 2000 that includes annual monitoring of forest health and productivity of 72 aspen stands across the western Canadian interior. Tree-ring analysis was conducted to determine the magnitude and cause of temporal variation in stand growth of aspen at the scale (1800 km × 500 km area) encompassed by this study. The results showed that during 1951–2000 the region's aspen forests underwent several cycles of reduced growth, notably between 1976 and 1981, when mean stand basal area increment decreased by about 50%. Most of the growth variation was explained by interannual variation in a climate moisture index in combination with insect defoliation. The results of the analysis indicate that a major collapse in aspen productivity likely occurred during the severe drought that affected much of the region during 2001–2003.

Inoptimality losses in forest management decisions caused by errors in an inventory based on airborne laser scanning and aerial photographs

2010 ◽  
Vol 40 (12) ◽  
pp. 2427-2438 ◽  
Author(s):  
Md. Nurul Islam ◽  
Mikko Kurttila ◽  
Lauri Mehtätalo ◽  
Timo Pukkala
Keyword(s):  
Input Data ◽  
Laser Scanning ◽  
Basal Area ◽  
Airborne Laser Scanning ◽  
Aerial Photographs ◽  
Stand Age ◽  
Inventory Data ◽  
Airborne Laser ◽  
Mean Diameter ◽  
The Mean

Errors in inventory data may lead to inoptimal decisions that ultimately result in financial losses for forest owners. We estimated the expected monetary losses resulting from data errors that are similar to errors in laser-based forest inventory. The mean loss was estimated for 67 stands by simulating 100 realizations of inventory data for each stand with errors that mimic those in airborne laser scanning (ALS) based inventory. These realizations were used as input data in stand management optimization, which maximized the present value of all future net incomes (NPV). The inoptimality loss was calculated as the difference between the NPV of the optimal solution and the true NPV of the solution obtained with erroneous input data. The results showed that the mean loss exceeded €300·ha–1 (US$425·ha–1) in 84% of the stands. On average, the losses increased with decreasing stand age and mean diameter. Furthermore, increasing errors in the basal area weighted mean diameter and basal area of spruce were found to significantly increase the loss. It has been discussed that improvements in the accuracy of ALS-based inventory could be financially justified.

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