119,107 research outputs found
Nation-wide clear-cut mapping in Sweden using ALOS PALSAR strip images
No full textAdvanced Land Observing Satellite (ALOS) Phased Array L-band type Synthetic Aperture Radar (PALSAR) backscatter images with 50 m pixel size (strip images) at HV-polarization were used to map clear-cuts at a regional and national level in Sweden. For a set of 31 clear-cuts, on average 59.9% of the pixels within each clear-cut were correctly detected. When compared with a one-pixel edge-eroded version of the reference dataset, the accuracy increased to 88.9%. With respect to statistics from the Swedish Forest Agency, county-wise clear-felled areas were underestimated by the ALOS PALSAR dataset (between 25% and 60%) due to the coarse resolution. When compared with statistics from the Swedish National Forest Inventory, the discrepancies were larger, partly due to the estimation errors from the plot-wise forest inventory data. In Sweden, for the time frame of 2008–2010, the total area felled was estimated to be 140,618 ha, 172,532 ha and 194,586 ha using data from ALOS PALSAR, the Swedish Forest Agency and the Swedish National Forest Inventory, respectively. ALOS PALSAR strip images at HV-polarization appear suitable for detection of clear-felled areas at a national level; nonetheless, the pixel size of 50 m is a limiting factor for accurate delineation of clear-felled areas
Stereo Evaluation of ALOS/PRISM Data on ESA-AO Test Sites - First DLR Results
No full textDLR's Remote Sensing Technology Institute has more than 20 years of history in developing spaceborne stereo scanners (MEOSS, MOMS) and the corresponding stereo evaluation software systems. It takes part in the ESA/JAXAAO Program to evaluate the performance and potential of the three-line stereo scanner PRISM (Panchromatic Remotesensing Instrument for Stereo Mapping) and the multispectral imaging sensor AVNIR-2 onboard the Japanese satellite ALOS as a principal investigator. French (near Marseille), German (near Munich) and Spanish (near Barcelona) test sites are proposed. In this paper, the process of direct georeferencing according to JAXA is shown and the results are presented. The geolocation accuracy improved immensely. For the newest dataset, ground control points (GCPs) are no
longer obligatory, but useful. Rational polynomial coefficients (RPCs) are generated using DLR software. Thereby, oscillations in the orientation angles in the order of up to one pixel on the ground occurred in the older datasets. These oscillations can not be compensated by an RPC-based approach, however, in the newer dataset, they are no longer existent. The coregistration of forward, nadir and backward view is examined and DSMs are generated and analyzed
Processors for ALOS Optical Data: Deconvolution, DEM Generation, Orthorectification, and Atmospheric Correction
No full textThe German Aerospace Center (DLR) is responsible for the development of prototype processors for PRISM and AVNIR-2 data under a contract of the European Space Agency. The PRISM processor comprises the radiometric correction, an optional deconvolution to improve image quality, the generation of a digital elevation model, and orthorectification. The AVNIR-2 processor comprises radiometric correction, orthorectification, and atmospheric correction over land. Here, we present the methodologies applied during these processing steps as well as the results achieved using the processors
Kajian Karakteristik Backscatter ALOS PALSAR Resolusi 50 Meter dan 12,5 Meter pada Perkebunan Karet dan Kelapa Sawit.
No full textThe study was performed to explore the relationship between the dimensions of rubber and oil palm plantations and backscatter of ALOS PALSAR having resolution 50 meters and 12.5 meters. The study was carried out in Simalungun Regency, Serdang Bedagai Regency, Asahan Regency and Pematang Siantar City North Sumatra Province. The main objective of the study is to identify crop variables that affect backscatter value. The study found that the rubber plantation variable that significantly affect the magnitude of backscatter of 50 meter resolution are the diameter at breast high (dbh) and basal area giving an accuracy of 75.44%. For oil palm plantation, the backscatter value was affected by canopy diameter with accuracy of 92.16%. For rubber plantation, the variable that affect the magnitude of backscatter of 12.5 meter resolution are the tree diameters, biomass volume and the ratio of crop spacing as well as canopy area with an accuracy of 66,67%. Meanwhile, for oil palm plantation, it was affected by height of plant with an accuracy of 62.75%.Sensor radar (radio detection and ranging) merupakan sensor gelombang mikro aktif (microwave) yang memungkinkan untuk melakukan pengamatan permukaan bumi dengan baik. Sensor ini mampu menembus awan, partikel hujan dan mempunyai sumber energi sendiri sehingga mampu melakukan pencitraan baik siang maupun malam dan pada segala macam cuaca. Sampai sekarang telah banyak satelit radar yang dioperasikan menyusul SEASAT, salah satunya adalah ALOS PALSAR. ALOS PALSAR merupakan citra radar yang bekerja pada saluran band-L dengan polarimatrik penuh HH, HV, VV dan VH. Lebar cakupan areal antara 250 sampai 350 km. Sensor dengan band L mampu menembus vegetasi hutan mulai dari daun, ranting, cabang dan bahkan sampai ke batang tanaman. Kemampuan citra ALOS PALSAR menembus vegetasi hutan sampai ke batang tanaman atau tumbuhan bawah akan berpengaruh terhadap sinyal pancar balik (backscatter) pada setiap tutupan lahan, dalam hal ini adalah tutupan lahan perkebunan karet dan perkebunan kelapa sawit. Penelitian ini mempunyai tujuan mengidentifikasi dimensi tanaman perkebunan karet dan perkebunan kelapa sawit yang mempengaruhi nilai backscatter citra ALOS PALSAR resolusi 50 meter dan 12,5 meter
Interferometric performance aspects for Tandem-L
No full textDLR is studying a future L-band satellite mission (Tandem-L) in close cooperation with NASA/JPL (DESDynI). This mission is designed to serve a variety of applications covering Solid Earth, forests, ice, etc. through the use of several SAR techniques.
We deal here with some aspects that concern Solid Earth applications and interferometry. The combination of high target coherence and the instrument large mapping capabilities calls for investigations into possible interferometric
processing schemes and their associated performance.
We discuss the extent of the degradations that are introduced with respect to the theoretical bounds when only multilooked interferograms between successive images are used. Improvements can be obtained by buffering a limited number of images and interferograms, depending on the decorrelation type
Kajian karakteristik backscatter citra ALOS PALSAR pada tegakan hutan tanaman eucalyptus grandis
No full textThis study was performed to identify the relationship beetwen the backscatter of ALOS PALSAR having pixel size of 50 x 50 m and 6,25 x 6,25 m, and the variables of Eucalyptus grandis forest plantation stand. The main objective of the study is to identify the variables that affect backscatter value. The study was carried out in Samosir Regency, North Sumatera Province. This study found that the variable of stands that influence the backscatter are (1) basal area height of tree having classification accuracy of 61.7 %. for resolution of 50 meters; and (2) acreage of tree canopy and trees density and the classification accuracy of 85. %. for resolution 6.25 meters.Satelit radar (radio detection and raging) merupakan sensor gelombang mikro (microwave) yang memungkinkan untuk melakukan perekaman permukaan bumi pada segala cuaca, baik siang maupun malam. Radar telah dikembangkan dengan pesat sejak dioperasikannya SEASAT, yaitu SIR-A, SIR-B, SIR-C, ERS-1, ERS-2, ALMAZ, JERS-1, RADARSAT dan ALOS PALSAR. Citra satelit tersebut beberapa telah digunakan dalam penelitian. Harrell et al. (1995) melakukan penelitian terhadap sensitifitas citra ERS-1 band C dan JERS-1 band L terhadap biomasa dan struktur tegakan. Selanjutnya Herman dan Dool (2005) menggunakan citra radar ERS-1 dan ERS-2 untuk penelitian karakteristik kekasaran permukaan dan tekstur sedimen. Hasil penelitian ini menunjukkan bahwa ada korelasi negatif antara backscatter dengan kandungan lumpur, serta korelasi positif yang signifikan antara backscatter dengan ukuran butir sedimen
ALOS PALSAR verification processor
No full textThis paper presents a verification processor, developed under ESA contract, for the generation of polarimetric, interferometric and polarimetric-interferometric geocoded products derived from SAR data obtained from the ALOS PALSAR instrument.
The processor, developed with a modular approach, contains the following main elements:
- Phase-preserving fine resolution processor; - Phase-preserving ScanSAR processor;
- Interference removal tools;
- Polarimetric calibration tools;
- Polarimetric analysis tools;
- Fine resolution interferometric processor; - ScanSAR interferometric processor;
- Polarimetric-interferometric processor;
- Geocoding;
- Atmospheric modelling tools.
All of the PALSAR acquisition modes (i.e. stripmap in one, two and full polarisations as well as ScanSAR) are supported both starting from raw and focused data.
The processor architecture is presented; highlights are given on modules and algorithms specifically developed for handling the peculiarities of these L-Band SAR data. Examples are shown obtained during the first year of operation of the system, over a number of test sites and of different types of products and acquisition modes
Measuring Azimuth Deformation With L-Band ALOS-2 ScanSAR Interferometry
No full textWe analyze the methods for measuring azimuth deformation with the L-band Advanced Land Observing Satellite-2 (ALOS-2) scanning synthetic aperture radar (ScanSAR) interferometry. To implement the methods, we extract focused bursts from the ALOS-2 full-aperture product, which is the only product available for ScanSAR interferometry at present. The extracted bursts are properly processed to measure azimuth deformation using interferometric phase. We apply the range split-spectrum method to ScanSAR to estimate the differential ionospheric phase of the interferogram, and take the azimuth derivative of the differential ionospheric phase to mitigate the relative azimuth shift caused by ionosphere. For the first time, azimuth deformation of a large earthquake (April 25, 2015 Nepal earthquake) is nearly completely measured by the L-band ScanSAR interferometry with moderate precision. The result is validated by the azimuth deformation measured by incoherent cross correlation using a pair of high-resolution RADARSAT-2 images. In addition to the final azimuth deformation, we show the possibility of processing full-aperture ScanSAR product using a burst-by-burst approach to form regular interferograms. We also show the recent strong large-scale ionospheric effects on the L-band ALOS-2 ScanSAR interferograms. Other possible applications of this paper include measuring the movement of glaciers
Iceberg Detection with L-Band ALOS-2 Data Using the Dual-POL Ratio Anomaly Detector
No full textIcebergs represent a danger to navigation in cold waters. Detection and tracking of large icebergs using space-borne scatterometers, altimeters and synthetic aperture radar (SAR) systems have seen a large amount of work in the last decades. However, the identification of small icebergs is still challenging especially when these are embedded in sea ice. In this work, a recently proposed iceberg detector the intensity Dual-Pol Ratio Anomaly Detector (iDPolRAD) is tested using ALOS-2 L-band data. The detector is designed for dual-polarized incoherent SAR images, however in this work we want to investigate the loss of performance with respect to using coherent data. Therefore different versions of the iDPolRAD requiring quad-pol data are proposed here and tested. The ALOS-2 data were acquired on the East Coast of Greenland, where a large number of icebergs are visible in the images. The results show that different polarisations could bring different information and therefore the availability of dual-pol could improve the detection although a quad-pol algorithm will not be operational at the moment due to the limited size of the swath
ALOS PALSAR Products Verification
No full textALOS, an enhanced successor of the Japanese Earth Resources Satellite 1 (JERS-1), was launched from JAXA’s Tanegashima Space Center in January 2006. ALOS operates from a sun-synchronous orbit at 691 km, with a 46-day recurrence cycle carrying a payload of three remote sensing instruments: the Panchromatic Remote Sensing Instrument for Stereo Mapping (PRISM) , the Advanced Visible and Near-Infrared Radiometer type 2 (AVNIR-2) and the polarimetric Phased Array L-band Synthetic Aperture Radar (PALSAR). The PALSAR sensor has the capacity to operate with a wide range of off-nadir angles and resolutions in a single-, dual-, and quad-pol mode.
An important contribution to the ALOS mission is the verification of PALSAR products to be distributed by the European ADEN node using the PALSAR processor developed by JAXA. Under contract to ESA/ESRIN the Microwaves and Radar Institute at the German Aerospace Center (DLR) Oberpfaffenhofen and its partners BAE Systems Advanced Technology Centre and CREASO GmbH developed a quality assessment tool (CALIX) for the verification of standard ALOS PALSAR products and also provided support for the verification for the ALOS PALSAR data quality. In addition, a set of corner reflectors and transponders have been deployed at the DLR test site Oberpfaffenhofen throughout the whole commissioning phase to allow an accurate measure of the basic product quality parameters.
The quality assessment features of the CALIX software include a product reader, antenna pattern estimation, point target analysis, distributed target analysis, geometric analysis and polarimetric analysis. Results obtained with CALIX on a set of products acquired over the DLR test site will be presented in this paper.
Since PALSAR is the first fully polarimetric spaceborne L-band sensor, propagation effects are important new issues to be addressed. The main challenge is to assess the influence of the ionosphere on the polarisation. Different approaches for estimating the Faraday rotation angle have been applied and the results are here compared
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