Publications in the field of Earth observation to support humanitarian operations
Braun, A. (2021): Extraction of Dwellings of Displaced Persons from VHR Radar Imagery – A Review on Current Challenges and Future Perspectives. GI_Forum 2021 9(1), 201 - 208.
While many studies exist to identify buildings from optical satellite images, radar-based approaches are still lacking in humanitarian contexts. This article outlines the main challenges related to scattering mechanisms returning from huts, tents, informal dwellings, and their natural surroundings, but also from geometric distortions caused by the side-looking radar aperture. An outlook summarizes how these limitations can be overcome by image enhancement or multi-image composites, but also by advanced methods on building extraction, such as convolutional neural networks (CNNs). This article aims to stimulate scientific debate and to lay a foundation for the development of new methods. Link
Braun, A. (2020): Supporting humanitarian missions with ALOS PALSAR-2. Poster presentation on the Joint PI Meeting of JAXA Earth Observation Missions in January 2021 (online).
Background Spaceborne radar images have become increasingly important for humanitarian organizations because they reliably deliver information in areas of crisis and allow quick response in case of emergency. This poster presents selected application examples based on ALOS PALSAR-2 products which were jointly developed with NGOs such as Doctors Without Borders, Action Against Hunger, or Groundwater Relief.
Gao, Y., Lang, S., Tiede, D., Wendt, L., & Workineh, G. (2021). Suggestions on the Selection of Satellite Imagery for Future Remote Sensing-Based Humanitarian Applications. GI_Forum 2021, 9, 228-236.
While many studies exist to identify buildings from optical satellite images, radar-based approaches are still lacking in humanitarian contexts. This article outlines the main challenges related to scattering mechanisms returning from huts, tents, informal dwellings, and their natural surroundings, but also from geometric distortions caused by the sidelooking radar aperture. An outlook summarizes how these limitations can be overcome by image enhancement or multi-image composites, but also by advanced methods on building extraction, such as convolutional neural networks (CNNs). This article aims to stimulate scientific debate and to lay a foundation for the development of new methods. Link
Gella, G.W., Wendt, L., Lang, S., Braun, A., Tiede, D., Hofer, B., Gao, Y., Schwendemann, G. (2021). Testing Transferability of Deep-Learning-Based Dwelling Extraction in Refugee Camps. GI_Forum 2021, 9, 220-227.
For effective humanitarian response in refugee camps, reliable information concerning dwelling type, extent, surrounding infrastructure, and respective population size is essential. As refugee camps are inherently dynamic in nature, continuous updating and frequent monitoring is time and resource-demanding, so that automatic information extraction strategies are very useful. In this ongoing research, we used labelled data and highresolution Worldview imagery and first trained a Convolutional Neural Network-based U-net model architecture. We first trained and tested the model from scratch for Al Hol camp in Syria. We then tested the transferability of the model by testing its performance in an image of a refugee camp situated in Cameroon. We were using patch size 32, at the Syrian test site, a Mean Area Intersection Over Union (MIoU) of 0.78 and F-1 score of 0.96, while in the transfer site, MIoU of 0.69 and an F-1 score of 0.98 were achieved. Furthermore, the effect of patch size and the combination of samples from test and transfer sites are investigated. Link
Gella, G. W., Wendt, L., Lang, S., Tiede, D., Hofer, B., Gao, Y., & Braun, A. (2022). Mapping of Dwellings in IDP/Refugee Settlements from Very High-Resolution Satellite Imagery Using a Mask Region-Based Convolutional Neural Network. Remote Sensing, 14(3), 689.
Earth-observation-based mapping plays a critical role in humanitarian responses by providing timely and accurate information in inaccessible areas, or in situations where frequent updates and monitoring are required, such as in internally displaced population (IDP)/refugee settlements. Manual information extraction pipelines are slow and resource inefficient. Advances in deep learning, especially convolutional neural networks (CNNs), are providing state-of-the-art possibilities for automation in information extraction. This study investigates a deep convolutional neural network-based Mask R-CNN model for dwelling extractions in IDP/refugee settlements. The study uses a time series of very high-resolution satellite images from WorldView-2 and WorldView-3. The model was trained with transfer learning through domain adaptation from nonremote sensing tasks. The capability of a model trained on historical images to detect dwelling features on completely unseen newly obtained images through temporal transfer was investigated. The results show that transfer learning provides better performance than training the model from scratch, with an MIoU range of 4.5 to 15.3%, and a range of 18.6 to 25.6% for the overall quality of the extracted dwellings, which varied on the bases of the source of the pretrained weight and the input image. Once it was trained on historical images, the model achieved 62.9, 89.3, and 77% for the object-based mean intersection over union (MIoU), completeness, and quality metrics, respectively, on completely unseen images. Link
Kugler, T., & Wendt, L. (2021). Evaluation of digital elevation models derived from multi-date satellite stereo imagery for urban areas. GI_Forum, 9(1), 60-67.
For the generation of 3D city models from satellite stereo imagery beyond the generation of digital surface models (DSM) from stereo data the next crucial step is the separation of urban 3D objects from ground. To do this the most common method is the derivation of a so called digital terrain model (DTM) from the DSM. The DTM should ideally contain only the surface of the ground on which the urban objects are located. Since only the surface of the objects can be seen from space, sophisticated methods have to be developed to gain information of the bare ground. In this paper selected methods for the extraction of a DTM from a DSM are described and evaluated. The evaluation is done by applying the methods to synthetically generated DSMs. These synthetical DSMs are a combination of ground and typical urban objects put on top of it. The application of the DTM extraction methods should recover in turn the original ground model as good as possible. Also the sum of the obtained DTM and the proﬁle of the urban objects should reconstruct the original DSM. The proﬁle of the urban objects ist often referenced as normalized digital elevation model (nDEM). But in general the equation DSM = DTM + nDEM is not always valid – especially for buildings situated on the slope of a hill. If the nDEM would simply be the difference of DSM – DTM the slope of the hill – contained in the DTM – will be reﬂected on the roof of the buildings. So also an advanced method for derivation of the nDEM from DSM and DTM is presented and tested. Link
Lang, S., L. Wendt, D. Tiede, Y. Gao, V. Streifeneder, H. Zafar, A. Adebayo, G. Schwendemann and P. Jeremias (2021). “Multi-feature sample database for enhancing deep learning tasks in operational humanitarian applications.” GI Forum – Journal for Geographic Information Science 9(1): 209-219.
Amongst the many benefits of remote sensing techniques in disaster- or conflict-related applications, timeliness and objectivity may be the most critical assets. Recently, increasing sensor quality and data availability have shifted the attention more towards the information extraction process itself. With promising results obtained by deep learning (DL), the notion arises that DL is not agnostic to input errors or biases introduced, in particular in sample-scarce situations. The present work seeks to understand the influence of different sample quality aspects propagating through network layers in automated image analysis. In this paper, we broadly discuss the conceptualisation of such a sample database in an early stage of realisation: (1) inherited properties (quality parameters of the underlying image such as cloud cover, seasonality, etc.); (2) individual (i.e., per-sample) properties, including a. lineage and provenance, b. geometric properties (size, orientation, shape), c. spectral features (standardized colour code); (3) context-related properties (arrangement Several hundred samples collected from different camp settings were hand-selected and annotated with computed features in an initial stage. The supervised annotation routine is automated so that thousands of existing samples can be labelled with this extended feature set. This should better condition the subsequent DL tasks in a hybrid AI approach. Link
Ostermann, F. O., Nüst, D., Granell, C., Hofer, B., & Konkol, M. (2021). Reproducible research and GIScience: An evaluation using GIScience conference papers. In Leibniz International Proceedings in Informatics, LIPIcs (Vol. 208, p. VII). Schloss Dagstuhl- Leibniz-Zentrum für Informatik GmbH, Dagstuhl Publishing.
[Best Paper Award of the GIScience 2021 Conference]
GIScience conference authors and researchers face the same computational reproducibility challenges as authors and researchers from other disciplines who use computers to analyse data. Here, to assess the reproducibility of GIScience research, we apply a rubric for assessing the reproducibility of 75 conference papers published at the GIScience conference series in the years 2012-2018. Since the rubric and process were previously applied to the publications of the AGILE conference series, this paper itself is an attempt to replicate that analysis, however going beyond the previous work by evaluating and discussing proposed measures to improve reproducibility in the specific context of the GIScience conference series. The results of the GIScience paper assessment are in line with previous findings: although descriptions of workflows and the inclusion of the data and software suffice to explain the presented work, in most published papers they do not allow a third party to reproduce the results and findings with a reasonable effort. We summarise and adapt previous recommendations for improving this situation and propose the GIScience community to start a broad discussion on the reusability, quality, and openness of its research. Further, we critically reflect on the process of assessing paper reproducibility, and provide suggestions for improving future assessments. Link
Riedler, B., Nödel, J., Siber, R., Andriessen, N., Strande, L., & Lang, S. (2021). Supporting urban sanitation management through the integration of EO-based indicators. abstract EARSEL joint workshop 2021: Earth Observation for sustainable cities and communities.
Sanitation refers to the provision of facilities and services for the safe disposal of human excrements and is included in SDG 6 “Ensuring the availability and sustainable management of water and sanitation for all”. With more than 2.5 billion people without appropriate facilities mainly living in cities, urban sanitation is critical to avoid harmful effects on human health and environment. Largely relying on onsite sanitation, the coordination of safe collection, treatment and disposal is essential. This requires reliable, up-to-date information that can be provided by EO data through its wide availability and objectivity. This is of particular importance in areas difficult to access and large, growing cities with urban sprawl. To facilitate the planning of faecal sludge management (FSM), priority areas where improvements are urgently needed can be identified using EO-based indicators, additionally enabling regular monitoring, evaluation of measures and targeted in-situ sampling. Link
Tiede, D., Schwendemann, G., Alobaidi, A., Wendt, L., Lang, S. (2021). Mask R‐CNN‐based building extraction from VHR satellite data in operational humanitarian action: An example related to Covid‐19 response in Khartoum, Sudan. Trans. GIS 25, 1213–1227.
Within the constraints of operational work supporting humanitarian organizations in their response to the Covid-19 pandemic, we conducted building extraction for Khartoum, Sudan. We extracted approximately 1.2 million dwellings and buildings, using a Mask R-CNN deep learning approach from a Pléiades very high-resolution satellite image with 0.5 m pixel resolution. Starting from an untrained network, we digitized a few hundred samples and iteratively increased the number of samples by validating initial classification results and adding them to the sample collection. We were able to strike a balance between the need for timely information and the accuracy of the result by combining the output from three different models, each aiming at distinctive types of buildings, in a post-processing workflow. We obtained a recall of 0.78, precision of 0.77 and F1 score of 0.78, and were able to deliver first results in only 10 days after the initial request. The procedure shows the great potential of convolutional neural network frameworks in combination with GIS routines for dwelling extraction even in an operational setting. Link
To be published...
Braun, A., Lang, S., Rogenhofer, E. (under review): Identification of refugee settlements by satellites of daily revisit time – A comparison of sensors and approaches. Turkish Journal of Humanitarian Action (submitted).
Braun, A. (submitted): Assessing risk of forcibly displaced persons: Creation of a digital elevation model of the island of Bhasan Char from Sentinel-1 Stripmap products. Living Planet Symposium 2022.
Gao, Y., Lang, S., Tiede, D., Wendt, L., & Workineh, G. (submitted) Assessing the validity of noisy label data in semantic segmentation for refugee dwelling extraction.
Lang, S. (submitted): Earth observation services for humanitarian action . Living Planet Symposium 2022.
Menk, L., Terzi, S., Zebisch, M., Rome, E., Lückerath, D., Milde, K., Kienberger, S. (submitted) “Climate Change Impact Chains: A Review of Applications, Challenges, and Opportunities for Climate Risk and Vulnerability Assessments”.
Riedler, B. & Lang, S. (submitted). Delineating and understanding urban structures through a multi-data source approach. Living Planet Symposium 2022.
Riedler B. & Lang S., (submitted), Towards integrating and assimilating geospatial datasets for urban structure ISPRS Annals of the Photogrammetry, Remote Sensing and Spatial Information Sciences.
Gella, G.W, Wendt, L, Braun, A., Tiede, D., Lang, S. (2021). Mask R-CNN based Mapping of Dwellings in Refugee Camps from High-Resolution Satellite Imagery. Abstract presented at 40th EARSeL Symposium 2021 European Remote Sensing-New Solutions for Science and Practice, Warsaw, Poland.