Thesis (MSc)--Stellenbosch University, 2000. / ENGLISH ABSTRACT: The aim of the study was to extract elevation information (such as tree height) from
stereo satellite imagery (IRS-I C), to scrutinise the performance of the DTM (Digital
Terrain Model) tools as provided by the LH (LeicalHelava) Systems' softcopy
system, and subsequently to perform a feasibility study on the application of a
practically viable forest inventory design.
A softcopy photogrammetry workstation (LH Systems DPW 770), IRS-I C stereo
panchromatic satellite imagery, and digital aerial photography at a scale of 1:30000
(scanned at 15 micrometers) was used. The study was conducted over various sites in
the Sabie area (province of Mpumalanga) in South Africa, where extensive man made
forests with pine and eucalypts are to be found. The extraction of stand parameters
such as tree height was performed manually, semi-automatically, and automatically.
In addition, the compartment area was determined using a GIS tool. The Digital
Surface Models (DSM), representing the canopy structure of the stands, was extracted
from the IRS-I C imagery and validated through a comparison of the resulting
contours with the corresponding contours generated by aerial photogrammetric
methods.
Due to the coarse spatial resolution of the IRS-IC imagery (5m) and the suboptimal
BIH (BaselHeight) ratio (0.57), only objects featuring a height exceeding 20m could
be manually measured with confidence. Furthermore, only the edges of the
compartments proved to be suitable for the determination of tree heights (i.e. with a
sufficiently large parallax difference and image contrast).
The manual determination of tree heights in the IRS-I C imagery yielded accuracies of
about 95% compared to the height values of the aerial photographs and the ground
data. The application of image enhancement techniques had severe effects on the
accuracy of the IRS-IC stereo model, resulting in deviations of about -57m from the
'true' value. It was observed that image matching was only a problem where features changed their appearance (e.g. clearfelled or burnt areas) during the acquisition period
of the stereo pair of the satellite imagery.
LH Systems' Adaptive Automatic Terrain Extraction (AATE) tool performed very
well for the creation of digital terrain and surface models when using digital aerial
photography with a high scanning rate. In contrast, the automatic creation of canopy
surface models from various forest compartments did not yield any useful results
when applied to IRS-l C imagery. AATE could not model the canopy structure
properly. The coarse spatial resolution of the satellite imagery in conjunction with the
sparse post spacing (20m) and matching errors are most likely to be responsible for
this poor performance.
Two-phase sampling and the Hugershoff method were chosen for automatically
derived height values to be evaluated for possible application in forest inventory.
Unfortunately, neither for the determination of the regression estimator for the first
method, nor for the calculation of timber volume after application of the Hugershoff
method could any useful result be obtained. This is mostly due to the fact that image
matching errors and blunders (resulting in tree heights of -885m) were not properly
accounted for in the terrain extraction software. However, the outcomes for the
manual measurement of tree heights performed on the satellite imagery show that
under optimal conditions accuracies can be achieved similar to those for the height
determination in small scale aerial photographs, but at lower cost. The obtained height
values can then be used for the calculation of timber volume according to Eichhorn's
law.
Keywords: AATE, blunders, digital photogrammetry, DPW770, forest inventory,
Hugershoff IRS-l C, matching error, remote sensing, satellite
imagery, two-phase sampling / AFRIKAANSE OPSOMMING: N GANGBAARHEIDSTIIDIE VIR BOSINVENTARIS MET BEHULP VAN
STEREO SATELLIETBEELDE MET GEBRUIK VAN SAGTEKOPIE
FOTOGRAMMETRIESETEGNOLOGIE: Die doel van hierdie studie was om elevasie inligting (soos boomhoogtes) uit stereo
satellietbeelde (IRS-I C) te ontrek, en die DTM (Digitale Terrein Modelle) funksies van
die LH Systems se sagtekopie sisteem te evalueer en 'n ondersoek in te stel na praktiese
toepassing van die tegnologie in bosvoorraadopname.
'n Sagtekopie fotogrammetriese werkstasie (LH Systems DPW 770), IRS-I C stereo
panchromatiese satellietwaarneming en digitale lugfotografie is gebruik. Die studie is
uitgevoer oor verskeie areas in die Sabie omgewing (Mpumalanga, Suid-Afrika), waar
daar ekstensiewe mensgemaakte woude voorkom met denne en Eucalyptus soorte. Die
ekstraksie van opstandparameters soos boomhoogte is uitgevoer met die hand, as ook met
semi-outomatiese en outomatiese metodes. Die digitale oppervlakmodelle (wat die
kroondakstrukture van die opstande voorstel) was vanaf die IRS-I C beelde onttrek en
gevalideer deur vergelyking van die resulterende kontoere met die korresponderende
kontoere wat deur lugfotogrammetriese metodes gegenereer is. As gevolg van die
growwe ruimtelike resolusie van die IRS-IC waarneming (Sm) en die suboptimale BIH
verhouding (0.57) kan slegs voorwerpe met 'n hoogte van meer as 20m met vertroue met
die hand gemeet word. Slegs die rande van die vakke is bruikbaar vir die berekening van
boomhoogtes (d.w. s. met 'n voldoende paralaksverskil en 'n sterk beeldkontras ).
Boomhoogtes wat met die hand bepaal is vanaf IRS-I C beelde is 95% akkuraat in
vergelyking met die hoogtewaardes verkry vanaf die lugfoto's en die veldmetings. Die
toepassing van beeldverbeteringstegnieke het duidelike invloede op die akkuraatheid van
die IRS-IC stereomodel met afwykings van ongeveer -57m vanaf die "werklike"
waardes. Daar is ook waargeneem dat beeldooreenstemming slegs 'n probleem is waar
terreinvorme se voorkoms verander het (weens afkappings of brande) gedurende die
verkrygingsperiode waarin die stereo paar van die satellietbeelde verkry is. LH Systems se Aanpassende Outomatiese Terrein Onttrekkings (Adaptive Automatic
Terrain Extraction - AATE) instrument het goed gevaar tydens die gebruik van digitale
lugfotografie met Inhoë skanderingstempo.
In kontras hiermee het die outomatiese skepping van kroondakoppervlakmodelle van
verskeie plantasievakke geen nuttige resultate gelewer wanneer dit op IRS-I C beelde
toegepas is nie. Die growwe ruimtelike resolusie van die satellietbeelde tesame met die
wye paalspasïering (20m) en passingsfoute is waarskynlik vir hierdie swak resultate
verantwoordelik.
Twee-fase proefueming en die Hugershoff metode was gebruik vir die bepaling van
outomaties afgeleide hoogtewaardes vir evaluering van moonlike toepassing in
bosvoorraadopnames. Geen bruikbare resultate kon verkry word vir die vasstelling van
die regressieskatter vir die eersgenoemde metode of vir die berekening van die
houtvolume volgens die Hugershoff metode nie. Dit is meestal as gevolg van beeld--
ooreenkomsfoute en flaters, (wat tot boomhoogtes van -885m gelei het) wat nie
voldoende in ag geneem word in die terreinekstraksie sagteware nie. Die resultate vir die
handgemete ('manual') boomhoogtebepaling wat uitgevoer is op die satellietbeelde (op
die sagtekopie werkstasie DPW 770), toon dat akkuraathede soortgelyk aan daardie vir
hoogte bepaal op klein-skaal lugfotos onder optimale toestande verkry kan word, maar
goedkoper. Die hoogtewaardes wat verkry is kan gebruik word vir die berekening van
houtvolume volgens die wet van Eichhorn.
Sleutelwoorde: AATE, afstandswaarneming, bosvoorraadopnames, digitale
fotogrammetrie, DPW770, flaters, Hugershoff, IRS-! C, satellietbeelde,
twee-fase proefueming
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/51609 |
| Date | January 2000 |
| Creators | Vogt, Holger K. H |
| Contributors | Bredenkamp, B., Katsch, H. C., Stellenbosch University. Faculty of AgriSciences. Dept. of Forest and Wood Science. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
| Format | 267 p. : ill. |
| Rights | Stellenbosch University |
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