La Tierra pudo ser habitable de forma intermitente

Details

Category: Actualidad

Hits: 677

Uno de los mayores misterios sobre la vida en la Tierra es su origen, cuándo y cómo se estableció, cómo consiguió desarrollarse y qué condiciones se dieron a la vez para que, finalmente, echara raíces y, un tiempo después, se multiplicara de una forma maravillosa hasta dar lugar a los millones de especies que existen en la actualidad, entre ellas seres inteligentes. Un equipo de la Universidad de Washington acaba de publicar un estudio en el que explica que los inicios de este proceso pudieron ser muy complejos. Según cuentan en la revista Proceedings of the National Academy of Sciences (PNAS), las condiciones adecuadas para albergar vida compleja pudieron haberse desarrollado en los océanos del joven planeta y luego desvanecerse más de mil millones de años antes de que la vida realmente se afianzara.

Los resultados, basados en el uso del elemento selenio como una herramienta para medir el oxígeno en el pasado distante, también pueden ayudar a buscar señales de vida fuera de la Tierra.

Michael Kipp, autor principal del estudio e investigador de Ciencias de la Tierra y del espacio, analizó las relaciones isotópicas del selenio en las rocas sedimentarias para medir la presencia de oxígeno en la atmósfera de nuestro mundo hace entre 2.000 y 2.400 millones de años, nada menos.

«Hay evidencia fósil de células complejas que se remontan quizá a 1.700 millones de años -explica Buick-. Sin embargo, el fósil más antiguo conocido no es necesariamente el más antiguo que haya existido, debido a que las posibilidades de ser preservados son bastante bajas».

Según el investigador, el estudio muestra que había suficiente oxígeno en el ambiente como para permitir que las células complejas evolucionaran, antes de que hubiera evidencia fósil. Por supuesto, eso no quiere decir que obligatoriamente lo hicieran, «pero podría ser», subraya Kipp.

La pista del selenio

Para llegar a esta conclusión, los científicos analizaron las trazas de selenio en trozos de pizarra sedimentaria de los períodos de tiempo determinados mediante espectrometría de masas en el Laboratorio de Geoquímica Isotópica de la universidad. Querían descubrir si el selenio había sido cambiado por la presencia del oxígeno, si se había oxidado. Los compuestos de selenio oxidados pueden verse reducidos, provocando un cambio en las relaciones isotópicas, que se graban en las rocas. La abundancia de selenio también aumenta en las rocas cuando una gran cantidad de oxígeno está presente.

Como explica Roger Buick, coautor del artículo, hasta ahora se pensaba que el oxígeno en la Tierra tenía un historial de «ninguno, alguno y después un montón. Pero lo que parece ahora es que hubo un período de un cuarto de mil millones de años de años más o menos en el que el oxígeno llegó bastante alto, y luego se hundió hacia abajo de nuevo».

La persistencia del oxígeno durante un largo período de tiempo es un factor importante. «Mientras que antes y después quizás habría entornos transitorios que podrían haber dado apoyo a estos organismos, para llegar a evolucionar y ser una parte importante del ecosistema se necesita que el oxígeno persista durante mucho tiempo», subraya Buick.

«La pregunta del millón»

Los investigadores creen que este aumento temporal del oxígeno fue moderadamente significativo en la atmósfera y la superficie del océano, pero no en las profundidades abisales. Qué hizo que los niveles de oxígeno se elevaran de esta manera para estrellarse tan drásticamente poco después «es la pregunta del millón de dólares», dice Eva Stüeken, también coautora del estudio e investigadora en la Universidad de St Andrews, en Escocia. «No se sabe por qué sucedió ni por qué terminó».

«Es un momento sin precedentes en la historia de la Tierra», afirma Buick. «Si nos fijamos en el registro de isótopos de selenio a través del tiempo, es un intervalo único. Si nos fijamos antes y después, todo es diferente».

Los investigadores creen que el selenio, utilizado como una herramienta eficaz para sondear los niveles de oxígeno en el pasado de la Tierra, también podría ser útil en la búsqueda de oxígeno -y quizás también de la vida- más allá de la Tierra. Las futuras generaciones de telescopios espaciales darán a los astrónomos información sobre la composición de la atmósfera de planetas lejanos. Algunos de ellos podrían tener aproximadamente el tamaño de la Tierra y potencialmente oxígeno apreciable en su atmósfera.

«El reconocimiento de un intervalo en el pasado distante de la Tierra que pudo haber tenido niveles de oxígeno casi modernos, pero muy diferentes habitantes biológicos, podría significar que la detección remota de un mundo rico en oxígeno no es necesariamente una prueba de una biosfera compleja», apunta Kipp. Sin embargo, «esta es una nueva forma de medir el oxígeno en el pasado histórico de un planeta, para ver si la vida compleja podría haber evolucionado allí y persistido el tiempo suficiente para convertirse en seres inteligentes», concluye Buick.

Apúntate a nuestra newsletter y recibe las noticias de Ciencia en tu correo todos los martes

Unmanned Aerial Systems for Cadastral Applications

Details

Category: Actualidad

Hits: 709

Testing a Fit-for-purpose Land Administration Approach in Indonesia

 

 

 

In recent decades, imagery-based methods have gained legitimacy in the domain of cadastral data creation. Contemporary experiences from Rwanda, Ethiopia and Lesotho, along with older activities from Thailand, already demonstrate the potential of conventional aerial imagery and high-resolution satellite imagery. More recently, unmanned aerial systems (UASs) have received increasing interest in the field of land administration. Already documented trials and demonstrations are evident for Albania, Namibia and Rwanda. The exploratory work continues; results from trials undertaken in Indonesia are presented here with a view to identifying the opportunities and challenges for embedding the technologies in a fit-for-purpose way into the existing cadastral processes.

By Sheilla Ayu Ramadhani, Ministry of Agrarian and Spatial Planning/National Land Agency (BPN), Indonesia, and Rohan Bennett and Francesco Nex, Faculty of Geo-Information Science and Earth Observation (ITC), The Netherlands

Indonesia’s existing cadastral data acquisition processes are coordinated by the National Land Agency (‘Badan Pertanahan Nasional’ or ‘BPN’). Methods employed are primarily terrestrial, including use of measuring tape, total stations and global navigation satellite systems (GNSSs). Indonesia has a challenging topography – often hilly and with dense vegetation – and this creates problems for terrestrial surveying methods.

The Imagery Opportunity

Imagery-based methods provide the opportunity to expedite the initial cadastral establishment process, which at current speeds suggests that four further decades of work are needed. However, use of imagery-based methods is not widely practised in the country, primarily due to the lack of base imagery at the required scale. UASs could help to sporadically fill specific gaps in the base map in a cost-effective and timely manner. Utilising the imagery developed, participatory mapping activities could be used to undertake the boundary mapping exercises.

Exploring Regulations

Many countries are actively developing – and redeveloping – rules for civilian and commercial UAS operation. In Indonesia, new regulations were issued in mid-2015 and these have implications for the use of UASs for cadastral purposes. The regulation defines restricted areas for UAS operation (e.g. flight operation areas) and also stipulates that UAS operation below 150 metres does not require registration. These rules need to be taken into account to ensure appropriate site selection and suitable flight planning. However, as yet, there are no specific rules for the use of UASs in cadastral applications – although, any UAS-based approach would need to adhere to existing cadastral requirements.

Designing a Workflow

Beyond clear understandings of the existing policies and legal frameworks relating to UASs and cadastres, a flowchart for UAS-based cadastral data collection was developed. It included an adaptive procedure of orthophoto generation and subsequent participatory mapping. A field test in Lunyuk Ode, Sumbawa, Indonesia, was conducted using a low-cost rotor UAS with an onboard low-cost camera. In addition, a methodology was developed to utilise the orthophotos and to encourage community participation in the delineation of parcel boundaries. The procedure was based upon participatory mapping approaches. Participatory mapping is designed for and by communities; it seeks the acknowledgement of all parties involved through the boundary agreements made in the field.

Flying and Creating

The test flight was planned in accordance with all legal and technical cadastral requirements. This resulted in a designed flight above the altitude of 70m with a high overlap setting: 90% forward overlap and 60% side overlap. Average ground sampling distance (GSD) was 2.99cm. In total, 532 images covering 32ha including around 240 parcels were captured. Using GNSS real time kinematic (RTK), 26 distributed ground control points were surveyed in order to improve the accuracy. The flight delivered output of imagery with 3cm horizontal accuracy, conducted within 720 minutes for five parcels and with costs of around USD80 for each parcel. The cost figures were derived using the Costing and Financing of Land Administration Services (CoFLAS) guidelines by the Global Land Tool Network (GLTN). It is suggested that the approach greatly overestimates the cost and time needed per parcel; when applied at a scale beyond a single pilot area, several key costs (e.g. equipment) would not scale as they are fixed.

Fit-for-purpose Evaluation

The entire process was evaluated against fit-for-purpose criteria including ‘participatory’, ‘attainable’, ‘reliable’ and ‘affordable’. Overall, good levels of adherence were measured; the process was considered participative and is considered to be reproducible. Compared with conventional approaches, the UAS-based method was shown to be more cost and time effective in creating parcel records. The approach also produced highly accurate spatial outputs. Whilst not explicitly evaluated, other fit-for-purpose criteria – ‘flexible’, ‘inclusive’ and ‘upgradable’ – appear to be supported by the approach. The approach can adjust to spatial accuracy needs, different purposes, temporal requirements, different user-group demands and geographical characteristics and can be used to upgrade qualities in a sporadic fashion over time. Taking the above into account, with regards to the participatory mapping approach, there are no (global) standard guidelines or prescribed quality control measures for conducting boundary surveys using imagery with community involvement. Further studies regarding this issue are needed: ones that consider quality assurance and issues of certainty, amongst other criteria.

Looking Ahead

In recent decades, Indonesia has made steady gains with respect to the spatial coverage of its cadastral system. However, much work remains to be done – particularly in the more remote, hilly and highly vegetated areas of the complex and diverse archipelago. The approach developed here is not intended as a panacea; UASs are not suitable for all cadastral applications. Instead, the mix of UASs and participatory mapping techniques offers a niche fit-for-purpose solution for specific areas and communities where land rights remain unrecorded, yet are legitimate and deserving of being formally acknowledged.     

Further Reading

• FIG (2014), Fit-For-Purpose Land Administration. FIG Publication No. 60, Copenhagen, Denmark

• GLTN (2015), Costing and Financing of Land Administration Services (CoFLAS) guidelines, UN-Habitat, Nairobi, Kenya.

• http://www.gim-international.com/content/article/uavs-revolutionise-land-administration

Sheilla Ramadhani
Quality and Control Analyst for Survey and Mapping in the Ministry of Agrarian and Spatial Planning/National Land Agency, Republic of Indonesia.

Rohan Bennett 
Director of the School for Land Administration Studies. Associate Professor at University of Twente, ITC Faculty, Netherlands. Project coordinator of Euro Commission Horizon2020 project ‘its4land’ (its4land.com).

Francesco Nex
Assistant Professor at University of Twente, ITC Faculty, The Netherlands. 
Chair of the ISPRS ICWG I/II on UAS & Small multi-sensor platforms: concepts & applications.

Este país necesita...

Details

Category: Actualidad

Hits: 550

Los profesionales de topografía en Colombia necesitamos unirnos con el fin de ser una comunidad solidaria que busque el bien del otro, nuestro propósito es crear entornos de colaboración mutua porque sabemos que trabajando en conjunto logramos grandes cosas. El país necesita equipos fortalecidos para solucionar los problemas concernientes al área de tierras y topografía.

Apúntate a la Cámara Colombiana de la Topografía 

Low-cost versus High-end Systems for Automated 3D Data Acquisition

Details

Category: Actualidad

Hits: 718

Modelling an Early Mediaeval Ring Fort in Germany

 

 

 

 

 

 

 

 

Topographic mapping is a standard surveying task and the instrument of choice used to be a total station. The use of terrestrial laser scanning has become popular over the past decade or more, but today there is a much wider choice of methods for the acquisition of a digital surface model (DSM). For the 3D recording of an early mediaeval ring fort, the use of three modern systems was investigated: a portable (kinematic) laser scanning system, a static terrestrial laser scanning system (TLS) and a photogrammetric unmanned aerial system (UAS). The systems were compared to each other based on the following criteria: efficiency and performance in the field, degree of automation for data processing, and accuracy achieved in relation to the system costs.

(By Maren Lindstaedt, Thomas P. Kersten and Klaus Mechelke, Hamburg, Germany)

The early mediaeval ring fort of Lembecksburg

The Lembecksburg ring fort is located on the North Sea island of Föhr (Figure 1), 1km north of the village of Borgsum. This circular earthwork was built on top of a geest, or slightly raised landform, next to the Föhrer Marsh. The outer diameter is 140m and the inner diameter is approximately 90m. The height is 10m above the outer ground, while on the inside the ground is only 3 to 4m below the wall top (Figure 1). In earlier times there was a ditch around the outside of the wall. This is difficult to identify today, although it is slightly visible in the east. Until the 19th century there was a tideway from the north of the wall to the Wadden Sea, which was presumably navigable for most of its length. The first construction of the wall dates back to the 8th century – the time of the Vikings – but traces of the Roman Empire (ceramics) have also been found at the archaeological site. Today the complete ring fort as well as the surrounding area is grass-covered.

Data Acquisition Methods and Systems Used

All data was collected by geomatics students from HafenCity University (HCU) in Hamburg, Germany, during a three-day measurement campaign. The reference data was surveyed using a Leica TCRA 1201 total station. A total of 550 topographic points were recorded covering the wall and the centre of the ring fort. For the static TLS data, the Zoller + Fröhlich IMAGER 5010 laser scanner was used. From 42 stations, an amount of about 12 million points per scan was acquired, which corresponds to a total number of approximately 504 million points and a scanning time of about 12 hours. For the registration of the scans at least five black and white targets per scan were used, which were determined by total station in a local coordinate system. The kinematic laser scanning was carried out with the ProScan system, provided and operated by the company p3d systems GmbHfrom Hamburg. This system is equipped with a TLS – in this case the IMAGER 5010 from HCU – plus a GNSS antenna and a high-precision inertial measurement unit from iMAR Navigation GmbH. Additionally, a GNSS reference station was needed for the system positioning, which was installed in the field close to the ring fort. To carry the 18kg system in object space, the sensor components were mounted on a special carrier known as a steadicam (camera stabiliser mount) used in the film industry (Figure 2). During walking the operator is able to control the system using a tablet PC. In total, four tracks were scanned in two hours by three operators, covering a length of 1,143m and an amount of 154 million points. For UAS photogrammetry a hexacopter Sky Hero Spy 750, equipped with a gimbal-mounted digital camera (Sony NEX-5, 16mm focal length, 14 megapixels), was used. 186 images were taken during an eight-minute flight, which was controlled manually rather than in automatic flight mode due to the strong gusting wind (Figure 3). For georeferencing of the image block, five targets for XYZ control points were distributed around the object and determined by total station.

Data Processing

The collected data was processed in such a way that similar and comparable datasets were obtained for each sensor. For the georeferencing of the point clouds, however, different processing procedures were implemented. For the p3d systems data the trajectories were calculated in the PCloud software in order to generate one point cloud for each track. The GNSS signal from the reference station was used to transform the data directly into UTM XY coordinates, while the height was adjusted by a constant shift. The positioning accuracy of the tracks was approximately 2 to 3cm. The static laser scans were georeferenced using the scanned targets; each station was registered using the target coordinates from total station measurements with a mean deviation of 2.4mm. The UAS image data was triangulated in Agisoft PhotoScan using five control points in a bundle adjustment for the determination of the image orientation and camera calibration parameters. The residuals of the control points after adjustment were less than one centimetre. The three different point clouds from kinematic TLS, static TLS and UAS photogrammetry were sampled down to 15cm point spacing. For the comparison, the ring fort itself plus an area of 40m around the ring fort was investigated. Each data volume was thus reduced to 1.2 million points. Finally, from each of the three point clouds, two datasets were derived for each sensor system. For the first, the point cloud was meshed in Geomagic with the 15cm point spacing, and for the second dataset a regular grid with 20cm point spacing was derived by filtering, where the lowest point was kept for each cell. In illustration, Figure 4 shows the mesh from the UAS data, which was filtered to a 20cm grid using only the lowest point.

Comparison of Derived Data

To obtain information about the accuracy of the DSM generated, the different models were compared to the reference data of the total station (Figure 5). Due to the long grass on the ground, which was estimated to be up to 40cm in height, significant differences are visible in all DSMs; none of the three tested methods is dominant. Assessing the meshed models without filtering achieved the following results:

The proportion of points having a maximum deviation of 20cm is 39% for the static TLS with IMAGER 5010, 43% for the UAS photogrammetry and 38% for the kinematic TLS from p3d systems. In comparison with the results for the filtered data, the proportion of points with max. 20cm deviation is higher for all methods, but not to a similar degree. The p3d systems dataset has improved significantly to 63%, the IMAGER 5010 dataset is now at 53%, while the UAS dataset shows a slight rise to 49% (Figure 6) Here it is clearly apparent that dense image matching is not able to generate ‘real’ ground points in the case of low vegetation such as grass or meadows. Nevertheless, the laser scanners have also problems with the grass height; on the one hand they deliver better results close to the scanning stations, but on the other hand points with increasing distance to the scanner station have similar deviations as the UAS data due to the scanner’s angle of incidence. Table 1 summarises the deviations in height against the reference dataset, including the amount of time spent on data acquisition and processing in relation to system costs.

Table 1, System costs, height differences compared with the reference dataset and amount of time involved in the three different measurement systems.

Conclusions

The authors investigated three different systems and methods for DSM generation and compared the achieved datasets against a reference dataset. Due to the long grass and vegetation, the mean deviations in height against the reference dataset were up to 30cm. Additional filtering of the datasets slightly improved the results, but could not eliminate the differences. Overall, the p3d systems dataset was evaluated to be the best one, followed by static laser scanning and UAS photogrammetry. Taking into account the time spent on data acquisition and processing, with a workload of five hours the kinematic TLS and the UAS photogrammetry are much more efficient methods than the static TLS which has a workload of 25 hours. It has to be assumed that in the case of less vegetation the UAS-generated data could obtain a similar quality in comparison to the kinematic TLS. Due to the low system costs, UASs are an alternative solution to static and mobile laser scanning. However, the slightly better results in this investigation were achieved by a high-end system costing approximately EUR 150,000, which might be an exclusion criterion for many applications.

Further Reading

• Kersten, Th., Lindstaedt, M., Mechelke, K., Omelanowsky, D., Prenting, J., 2016. Low-Cost vs. High-End Systeme im Vergleich – 3D-Aufnahme der Ringwallanlage Lembecksburg auf der Nordseeinsel Föhr (in German). Photogrammetrie, Laserscanning, Optische 3D-Messtechnik – Beiträge der Oldenburger 3D-Tage 2016, Th. Luhmann/Ch. Schumacher (Hrsg.), Wichmann, VDE Verlag GmbH, Berlin und Offenbach, pp. 150-161
  
  

Acknowledgements

The authors gratefully acknowledge the UAS flight by Dr Johannes Prenting from Aerophoto Hamburg, and the kinematic scanning with the ProScan system of p3d systems by Daniel Omelanowsky. The measurement support of the following bachelor students (geomatics) is also gratefully acknowledged: H. Depner, N. Kampf, K. Keilich, M. Kind, K. Kopczyk, A. Kosciuk, F. Sarabia and M. Spilker.

Biographies of the Authors

Maren Lindstaedt has been a teaching and research associate in the field of geomatics at HafenCity University Hamburg since 2004 after she graduated in geomatics from the Hamburg University of Applied Sciences.

Thomas P. Kersten has been a full professor for photogrammetry and laser scanning in the bachelor and master geomatics study programmes at HafenCity University Hamburg since 2001. He is also head of the Photogrammetry and Laser Scanning Lab there.

Klaus Mechelke has been a teaching and research associate in the field of geomatics at HafenCity University Hamburg since 1992.