Aspects of Accuracy, Scanning Angle Optimization, and Intensity Calibration Related to Nationwide Laser Scanning

Osajulkaisut: Publication 1: Ahokas, E., Kaartinen, H., Hyyppä, J. 2004. A quality assessment of repeated airborne laser scanner observations. The International Archives of Photogrammetry, Remote Sensing and Spatial Information Sciences, Istanbul, Turkey, Vol. XXXV, part B3, pp. 237-242. ISSN 1682-1750. Publication 2: Ahokas, E., Hyyppä, J., Kaartinen, H., Kukko, A., Kaasalainen, S., Krooks, A. 2010. The effect of biomass and scanning angle on laser beam transmittance. International Archives of Photogrammetry, Remote Sensing and Spatial Information Sciences, Vienna, Austria, Vol. XXXVIII(7A), pp. 1-6. ISSN 1682-1777. http://www.isprs.org/proceedings/XXXVIII/part7/a/pdf/1_XXXVIII-part7A.pdf Publication 3: Ahokas, E., Hyyppä, J., Yu, X., Holopainen, M. 2011. Transmittance of Airborne Laser Scanning Pulses for Boreal Forest Elevation Modeling. Remote Sensing. 3, 1365-1379. ISSN 2072-4292. http://www.mdpi.com/2072-4292/3/7/1365/ Publication 4: Kaasalainen, S., Ahokas, E., Hyyppä, J., Suomalainen, J. 2005. Study of surface brightness from backscattered laser intensity: Calibration of laser data. IEEE Geoscience and remote sensing letters, Vol. 2, No. 3, pp. 255-259, ISSN 1545-598X. Publication 5: Ahokas, E., Kaasalainen, S., Hyyppä, J., Suomalainen, J. 2006. Calibration of the Optech ALTM 3100 laser scanner intensity data using brightness targets. ISPRS Commission I Symposium, Paris Marne-la-Vallee, 4-6 July 2006, ISPRS Volume XXXVI Part 1/A. pp. 14-20. CD-ROM publication. Also in Revue Française de Photogrammétrie et de Télédétection, No. 182, (2006-2), pp. 10-16. Publication 6: Honkavaara, E., Peltoniemi J., Ahokas, E., Kuittinen R., Hyyppä, J., Jaakkola, J., Kaartinen, H., Markelin, L., Nurminen, K., Suomalainen, J. 2008. A Permanent Test Field for Digital Photogrammetric Systems. Photogrammetric Engineering and Remote Sensing. Vol. 74, No. 1, pp. 95-106.Airborne laser scanning is a technique that produces three-dimensional coordinates of the Earth’s surface as well as generating intensity values. Nationwide airborne laser scanning was launched in Finland in 2008 and some 180 000 km2 had been scanned by the end of 2012. While the main goal in this endeavour is to produce an accurate digital elevation/terrain model (2 x 2 m2 grid size) of the whole of the country, other applications, e.g. forestry, will benefit from the data as well. This study deals with the accuracy of airborne laser scanning, the optimization of the scanning angle, and the calibration of intensity. Accuracy assessments of airborne laser scanning have shown that the geometric accuracy of the method can fulfill the accuracy requirements for producing a nationwide digital elevation model with a grid of 2 x 2 m2. When studying the effect of scanning angle and biomass on elevation modeling capability, it was found that it would be possible to increase the scanning angle applied in Finland’s nationwide laser scanning. Even though the accuracy of the elevation model in the conditions prevailing in Finland allows increasing of the scanning angle, other applications would most probably not benefit from this. For example, these same data are sometimes used in nationwide forest inventory in Finland. A method for relative and absolute calibration of airborne laser scanning intensity was developed. The portable reference targets have proved their usefulness for calibration purposes. An intensity correction method should be used in pre-processing the airborne laser data. As a result of this, the usability of the intensity values may increase in practical applications, such as in classification. The studies constituting this dissertation have already impacted on the practical aspects of the nationwide airborne laser scanning dealing with accuracy assessment, the work done in the field of intensity calibration, and scanning angle analysis may have a further impact on nationwide laser scanning in the coming years. The optimization of airborne laser scanning flight parameters for multi-use nationwide laser scanning is a topic deserving further research.Ilmasta tehtävä laserkeilaus tuottaa 3D-koordinaatteja maan pinnalta sekä intensiteettiarvoja. Suomen valtakunnallinen laserkeilaus aloitettiin vuonna 2008 ja noin 180000 km2 oli keilattu vuoden 2012 loppuun mennessä. Vaikka päätarkoituksena on tuottaa tarkka digitaalinen korkeus/maastomalli (2 x 2 m2 ruutukoko) koko maasta, muutkin sovellukset, kuten metsätalous, hyötyvät tästä aineistosta. Tämä tutkimus käsittelee ilmasta tehtävän laserkeilauksen tarkkuutta, keilauskulman optimointia sekä intensiteetin kalibrointia. Laserkeilauksen tarkkuusarviointi on osoittanut, että menetelmän geometrinen tarkkuus täyttää valtakunnallisen digitaalisen korkeusmallin tuottamisen tarkkuusvaatimukset. Kun tutkittiin keilauskulman ja biomassan vaikutusta korkeusmallin tuottamiseen, huomattiin että olisi mahdollista kasvattaa valtakunnallisen laserkeilauksen havaintokulmaa. Vaikka korkeusmallin tarkkuus mahdollistaisi Suomen oloissa keilauskulman kasvattamisen, muut sovellukset eivät luultavasti hyötyisi tästä. Esimerkiksi tätä samaa aineistoa käytetään Suomen valtakunnallisessa metsien inventoinnissa. Laserkeilauksen intensiteetin suhteellista ja absoluuttista kalibrointia varten kehitettiin menetelmä. Siirrettävät referenssikohteet osoittivat käyttökelpoisuutensa intensiteetin kalibroinnissa. Intensiteetin kalibrointimenetelmää tulisi käyttää laserkeilausaineiston esikäsittelyssä. Tämän tuloksena intensiteettiarvojen käyttökelpoisuus kasvaisi käytännön sovelluksissa, kuten luokittelussa. Tämän väitöskirjan muodostaneet tutkimukset ovat jo käytännössä vaikuttaneet valtakunnallisen laserkeilauksen tarkkuusarvioinnissa. Intensiteetin kalibrointityö ja keilauskulman analysointi vaikuttanevat valtakunnalliseen laserkeilaukseen tulevina vuosina. Lisätutkimusta tarvitaan ilmasta tehtävän laserkeilauksen lentoparametrien optimoimiseksi monikäyttöistä valtakunnallista laserkeilausta varten

Evaluating airborne laser data on steeply sloping terrain

Accuracy of Airborne Laser Terrain Mapping (ALTM) elevations is not well known on steeply sloping terrain. A unique method was used whereby, the planimetric location of ALTM ground strikes were located in the field and reference elevations measured at these points. Survey-grade Global Navigation Satellite System (GNSS) and rigorous techniques accurately established vertical heights to 0.010 meters, Root Mean Squared Error (RMSE). Sampled slopes range from 0.5 degrees to 50.6 degrees. A positive quadratic relationship exists between slope and vertical error. Error is negligible on slopes less than twenty degrees. Incidence angle, footprint size, and elevation spread from the upper reach of the footprint to the lower reach for each laser strike were also determined. An increase in each results in an increase in ALTM elevation imprecision. Elevation spread within the footprint and horizontal error could account for high percentages of vertical error on steeper slopes

BDS GNSS for Earth Observation

For millennia, human communities have wondered about the possibility of observing phenomena in their surroundings, and in particular those affecting the Earth on which they live. More generally, it can be conceptually defined as Earth observation (EO) and is the collection of information about the biological, chemical and physical systems of planet Earth. It can be undertaken through sensors in direct contact with the ground or airborne platforms (such as weather balloons and stations) or remote-sensing technologies. However, the definition of EO has only become significant in the last 50 years, since it has been possible to send artificial satellites out of Earth’s orbit. Referring strictly to civil applications, satellites of this type were initially designed to provide satellite images; later, their purpose expanded to include the study of information on land characteristics, growing vegetation, crops, and environmental pollution. The data collected are used for several purposes, including the identification of natural resources and the production of accurate cartography. Satellite observations can cover the land, the atmosphere, and the oceans. Remote-sensing satellites may be equipped with passive instrumentation such as infrared or cameras for imaging the visible or active instrumentation such as radar. Generally, such satellites are non-geostationary satellites, i.e., they move at a certain speed along orbits inclined with respect to the Earth’s equatorial plane, often in polar orbit, at low or medium altitude, Low Earth Orbit (LEO) and Medium Earth Orbit (MEO), thus covering the entire Earth’s surface in a certain scan time (properly called ’temporal resolution’), i.e., in a certain number of orbits around the Earth. The first remote-sensing satellites were the American NASA/USGS Landsat Program; subsequently, the European: ENVISAT (ENVironmental SATellite), ERS (European Remote-Sensing satellite), RapidEye, the French SPOT (Satellite Pour l’Observation de laTerre), and the Canadian RADARSAT satellites were launched. The IKONOS, QuickBird, and GeoEye-1 satellites were dedicated to cartography. The WorldView-1 and WorldView-2 satellites and the COSMO-SkyMed system are more recent. The latest generation are the low payloads called Small Satellites, e.g., the Chinese BuFeng-1 and Fengyun-3 series. Also, Global Navigation Satellite Systems (GNSSs) have captured the attention of researchers worldwide for a multitude of Earth monitoring and exploration applications. On the other hand, over the past 40 years, GNSSs have become an essential part of many human activities. As is widely noted, there are currently four fully operational GNSSs; two of these were developed for military purposes (American NAVstar GPS and Russian GLONASS), whilst two others were developed for civil purposes such as the Chinese BeiDou satellite navigation system (BDS) and the European Galileo. In addition, many other regional GNSSs, such as the South Korean Regional Positioning System (KPS), the Japanese quasi-zenital satellite system (QZSS), and the Indian Regional Navigation Satellite System (IRNSS/NavIC), will become available in the next few years, which will have enormous potential for scientific applications and geomatics professionals. In addition to their traditional role of providing global positioning, navigation, and timing (PNT) information, GNSS navigation signals are now being used in new and innovative ways. Across the globe, new fields of scientific study are opening up to examine how signals can provide information about the characteristics of the atmosphere and even the surfaces from which they are reflected before being collected by a receiver. EO researchers monitor global environmental systems using in situ and remote monitoring tools. Their findings provide tools to support decision makers in various areas of interest, from security to the natural environment. GNSS signals are considered an important new source of information because they are a free, real-time, and globally available resource for the EO community

UAVs for the Environmental Sciences

This book gives an overview of the usage of UAVs in environmental sciences covering technical basics, data acquisition with different sensors, data processing schemes and illustrating various examples of application

Adapting Construction Staking to Modern Technology

This report summarizes the tasks and findings of the ICT Project R27-163, Adapting Construction Staking to Modern Technology, which aims to develop written procedures for the use of modern technologies (such as GPS and civil information modeling) in construction staking of highway projects, for inclusion in the Illinois Department of Transportation’s (IDOT’s) Construction Manual. Six primary research tasks were completed: (1) conducting a comprehensive literature review on the use of modern technologies in construction staking by state departments of transportation (DOTs) and contractors; (2) conducting a survey to gather information from state DOTs and contractors on current practices employed by other states; (3) identifying a set of potential practices for employment in Illinois; (4) conducting a survey to gather feedback from IDOT staff and Illinois contractors; (5) developing draft summarized written procedures for review by the Technical Review Panel (TRP); and (6) developing complete written procedures for the use of modern technologies in construction staking of highway projects, for inclusion in IDOT’s Construction Manual. The written procedures are intended to support construction-staking processes when a contractor employs such technologies. The procedures are expected to enable the employment of these technologies in Illinois and, in turn, to offer major opportunities for quality improvements, cost savings, and expediting project delivery.IDOT-R27-163Ope

Journal of Applied Hydrography

Fokusthema: Fernerkundung und Laserbathymetri

Geodesy: The science underneath

Geodesy is the science of precisely measuring and mapping the Earth’s surface and locations of objects on it, the figure of the Earth and her gravity field, and changes in all these over time. Geodesy is an old science, going back to the days when land was taken into agricultural use and needed to be mapped. It is also a modern science, serving vital infrastructure needs of our developing global technological society. This text aims to describe the foundations of both traditional geodesy, mapping the Earth within the constraints of the human living space, and modern geodesy, exploiting space technology for mapping and monitoring our planet as a whole, in a unified threedimensional fashion. The approach is throughout at conveying an understanding of the concepts, of both the science and mathematics of measuring and mapping the Earth and the technologies used for doing so. The history of the science is not neglected, and the perspective of the presentation is unapologetically Finnish.Geodesia on tiede, joka mittaa ja kartoittaa tarkasti Maan pintaa ja sen päällä olevia kohteita, Maan muotoa ja painovoimakenttää, sekä niiden kaikkien ajallisia muutoksia. Geodesia on vanha tiede, joka oli olemassa jo muinoin kun maanviljely alkoi ja peltoja piti kartoittaa. Se on myös moderni tiede, joka palvelee modernin, kehittyvän globaalin teknologisen yhteiskuntamme olennaisia infrastruktuuritarpeita. Tämä kirja esittää sekä perinteisen että modernin geodesian perusteet. Perinteinen geodesia kartoittaa Maata ihmisen elintilan puitteissa ja sen ehdolla, kun moderni geodesia käyttää avaruusteknologiaa koko maaplaneetamme kartoittamiseksi ja seuraamiseksi yhtenäisellä kolmiulotteisella tavalla. Tavoitteena on auttaa Maan mittaamiseen ja kartoittamiseen liittyvien sekä tieteellis-matemaattisten että teknologisten käsitteiden ymmärtämistä. Geodesian historiaa ei unohdeta, ja kirjoitelman näkökulma on avoimesti suomalainen

Determining estuarine seagrass density measures from low altitude multispectral imagery flown by remotely piloted aircraft

Seagrass is the subject of significant conservation research. Seagrass is ecologically important and of significant value to human interests. Many seagrass species are thought to be in decline. Degradation of seagrass populations are linked to anthropogenic environmental issues. Effective management requires robust monitoring that is affordable at large scale. Remote sensing methods using satellite and aircraft imagery enable mapping of seagrass populations at landscape scale. Aerial monitoring of a seagrass population can require imagery of high spatial and/or spectral resolution for successful feature extraction across all levels of seagrass density. Remotely piloted aircraft (RPA) can operate close to the ground under precise flight control enabling repeated surveys in high detail with accurate revisit-positioning. This study evaluates a method for assessing intertidal estuarine seagrass (Zostera muelleri) presence/absence and coverage density using multispectral imagery collected by a remotely piloted aircraft (RPA) flying at 30 m above the estuary surface (2.7 cm ground sampling distance). The research was conducted at Wharekawa Harbour on the eastern coast of the Coromandel Peninsula, North Island, New Zealand. Differential drainage of residual ebb waters from the surface of an estuary at low tide creates a mosaic of drying sediment, draining surface and static shallow pooling that has potential to interfere with spectral observations. The field surveys demonstrated that despite minor shifts in the spectral coordinates of seagrass and other surface material, there was no apparent difference in image classification outcome from the time of bulk tidal water clearance to the time of returning tidal flood. For the survey specification tested, classification accuracy increased with decreasing segmentation scale. Pixel-based image analysis (PBIA) achieved higher classification accuracy than object-based image analysis (OBIA) assessed at a range of segmentation scales. Contaminating objects such as shells and detritus can become aggregated within polygon objects when OBIA is applied but remain as isolated objects under PBIA at this image resolution. There was clear separability of spectra for seagrass and sediment, but shell and detritus confounded the classification of seagrass density in some situations. High density seagrass was distinct from sediment, but classification error arose for sparse seagrass. Three classifiers (linear discriminant analysis, support vector machine and random forest) and three feature selection options (no selection, collinearity reduction and recursive feature elimination) were assessed for effect on classification performance. The random forest classifier yielded the highest classification accuracy, with no accuracy benefit gained from collinearity reduction or recursive feature elimination. Spectral vegetation indices and texture layers substantially improved classification accuracy. Object geometry made a negligible contribution to classification accuracy using mean-shift segmentation at this image-scale. The method achieved classification of seagrass density with up to 84% accuracy on a three-tier end-member class scale (low, medium, and high density) when using training data formed using visual interpretation of ground reference photography, and up to 93% accuracy using precisely measured seagrass leaf-area. Visual interpretation agreed with precisely measured seagrass leaf area 88% of the time with some misattribution at mid-density. Visual interpretation was substantially faster to apply than measuring the leaf area. A decile class scale for seagrass density correlated with actual leaf area measures more than the three-tier scale, however, was less accurate for absolute class attribution. The research demonstrates that seagrass feature extraction from RPA-flown imagery is a feasible and repeatable option for seagrass population monitoring and environmental reporting. Further calibration is required for whole- and multi-estuary application

Evaluating the Correctness of Airborne Laser Scanning Data Heights Using Vehicle-Based RTK and VRS GPS Observations

In this study, we describe a system in which a GPS receiver mounted on the roof of a car is used to provide reference information to evaluate the elevation accuracy and georeferencing of airborne laser scanning (ALS) point clouds. The concept was evaluated in the Klaukkala test area where a number of roads were traversed to collect real-time kinematic data. Two test cases were evaluated, including one case using the real-time kinematic (RTK) method with a dedicated GPS base station at a known benchmark in the area and another case using the GNSSnet virtual reference station service (VRS). The utility of both GPS methods was confirmed. When all test data were included, the mean difference between ALS data and GPS-based observations was −2.4 cm for both RTK and VRS GPS cases. The corresponding dispersions were ±4.5 cm and ±5.9 cm, respectively. In addition, our examination did not reveal the presence of any significant rotation between ALS and GPS data