Co-registration Of Optically Sensed Images And Correlation Research Articles

Annual velocities of the ablation zone of Panchi Nala Glacier, western Himalaya: Trends and controlling factors

Information on the glacier velocity is imperative to understand the glacier ice volume, supraglacial feature evolution and glacier-climate interaction. The present study investigates annual velocities of the ablation zone (∼4500–4800 m asl) of Panchi Nala Glacier, western Himalaya through feature tracking. For this, multi-temporal Landsat (TM and OLI) and Sentinel −2 MSI images, acquired between 2000 and 2021, were correlated using the Co-registration of Optically Sensed Images and Correlation (COSI-Corr) tool. Results reveal a mean velocity of the ablation zone to be 10.6 ± 5.6 m/y during 2000–2021, with the highest (13.8 ± 4.6 m/y) and lowest velocity (8.9 ± 2.8 m/y) observed in 2005 and 2015, respectively. There is no significant trend in the velocity, rather it is highly heterogeneous on the inter-annual scale. Further, the influence of several factors such as slope, debris cover, altitude, annual average temperature and precipitation on the glacier velocity was investigated. Results indicate that the inter-annual heterogeneity in velocity is inversely correlated with the variation of summer precipitation implying that an increase in summer precipitation decreases the glacier velocity. The spatio-temporal velocity variations are also linked with the presence of supraglacial ponds, ice cliffs and heterogeneous debris distribution over the glacier. Findings indicate that, though annual glacier velocities have not changed significantly, their magnitudes are consistently low which coupled with consistent debris increase (19.74%) and gentle slope (8.2° over ablation zone) can promote rapid growth of supraglacial ponds and ice cliffs.

Monitoring solifluction movement in space and time: A semi-automated high-resolution approach

Solifluction is the slow downslope movement of soil mass due to freeze-thaw processes. It is widespread on hillslopes in Polar and Alpine regions and contributes substantially to sediment transport. As solifluction lobe movement is in the order of millimeters to centimeters per year, it is difficult to measure with high spatial and temporal resolution and accuracy. In this study we developed a semi-automated approach to monitor movement using unmanned aerial vehicles, image co-alignment, and COSI-Corr (Co-registration of Optically Sensed Images and Correlation) to track slope movement from orthophotos. The method was applied on yearly images acquired between 2017 and 2021 of three solifluction lobes with different degrees of vegetation cover along an elevational gradient in Turtmann Valley, Swiss Alps. We found movement patterns across all three lobes with highest movement rates at the solifluction lobes center and lowest rates at lobe fronts. Overall, at the highest elevations (2560 m) lobe movement rates were highest with up to 14.0 cm yr−1 and intermediate elevations (2417 m) had the lowest values up to 2.9 cm yr−1. The lobe at the lowest elevation (2170 m) showed intermediate movement rates with up to 4.9 cm yr−1 for single years. Our monitoring approach provides yearly, spatially extensive movement estimates across the complete spatial extent of a lobe for each 1 cm2 of its surface, strongly increasing measurement resolution in comparison to traditional solifluction monitoring approaches using point measurements. In comparison to previous close-range remote sensing approaches, the use of a co-alignment procedure for the acquired drone data enabled a time-saving field setup without Ground Control Points (GCPs). The resulting high co-registration accuracy enabled us to detect solifluction movement if it exceeds 5 mm with sparse vegetation cover. Dense vegetation cover limited feature-tracking but detected movement rates and patterns are in the same order of magnitude and matched previous measurements using classical total station measurements at the lowest, mostly vegetated lobe. This study demonstrates the use of drone-based Digital Elevation Models (DEMs) and orthophotos in a semi-automated method which reaches the high spatiotemporal resolution necessary to detect subtle movements of solifluction lobes at yearly intervals at the sub-centimeter scale. This provides new insights into solifluction movement and how much it contributes to sediment transport. Therefore, our semi-automated approach has a great potential to uncover the fundamental processes and better understand solifluction movement.

Monitoring glacier characteristics and their mass balance using a multidimensional approach over the glaciers of the Chandra basin, western Himalaya

ABSTRACT Glacier change monitoring provides a significant understanding of glacier health and its influence on freshwater availability. Therefore, we have utilized remotely sensed data to estimate the glacier characteristics, mass balance, and volume change during 2013–2019 over the Sutri Dhaka and Batal glaciers, Chandra basin, western Himalayas. The glacier feature classification and shifting in isoline were mapped on a spatio-temporal scale. Furthermore, the surface velocity was measured using Coregistration of Optically Sensed Images and Correlation (COSI-Corr) and then used for estimating the ice thickness. The estimated velocity was compared with the stake observations and National Aeronautics and Space Administration (NASA)- Inter-Mission Time Series of Land Ice Velocity and Elevation (ITS_LIVE) data. Further, the glaciers’ geodetic mass balance and volume change were calculated, indicating an average value of −0.03 ± 0.5, −0.34 ± 0.40 and −0.13 ± 0.14 m water equivalent (w.e.) year−1 during 2000–2009, 2009–2020, and 2000–2020, respectively. This multidimensional analysis of the glaciers is critical, as the meltwater from both glaciers contributes to the Chandra basin and also influences the local ecosystem.

Determining the spatio-temporal variability of glacier surface velocity using high-resolution satellite images and UAV data: Alamkuh glacier, Iran

ABSTRACT In this study, multi-temporal high-resolution satellite and Unmanned Aerial Vehicle (UAV) images were obtained to determine glacier kinematics and dynamics for the first time in Iran, which could enhance our understanding of debris-covered glacier change mechanisms in this part of the world. the flow velocity change of Alamkouh debris-covered glacier in Iran was surveyed using the combination of very high-resolution satellite and UAV imageries from 2005 to 2020. Glacier surface velocity (GSV) during the last 15 years was analysed by employing the frequency cross-correlation technique using Co-registration of Optically Sensed Images and Correlation (COSI-Corr) module on Quickbird (2005), Wordview-2 (2010) and UAV images (2018 and 2020) for the periods 2005–2010, 2010–2018 and 2018–2020, respectively. Results indicate that the mean annual GSV does not remain constant and fluctuates in different periods without a clear and straightforward increasing or decreasing trend. The mean annual GSV in the whole part of the glacier area from 2005 to 2010 was about 1.06 m year−1. Then, it decreases to 0.69 m year−1 during 2010–2018 and finally, it increases to 1.08 m year−1 during 2018–2020. Spatially, monitoring glacier velocity change during the last fifteen years indicates that glacier activity decreased at the lowest part of the glacier and the velocity had increased with a rising altitude from the glacial tongue to the high elevation accumulation areas.

Glacier surface velocities in the Jankar Chhu Watershed, western Himalaya, India: Study using Landsat time series data (1992–2020)

This study presents a spatial and temporal surface velocity analysis of 33 glaciers in the Jankar Chhu Watershed (JCW), western Himalaya. The surface velocity was computed using the Co-registration of Optically Sensed Images and Correlation (COSI-Corr) tool on the Landsat images spanning nearly three decades (1992–2020). Long-term (1948–2018) inter-annual and seasonal climatic trends are also evaluated based on the US NCEP/NCAR reanalyzed gridded data. The role of several topographic and climatic parameters was examined to characterize heterogeneity in velocity.Glaciers in the JCW exhibit three distinct spatial velocity patterns. The type-I glaciers show nearly stagnant (<5 m yrˉ1) debris-covered tongues but a maximum velocity of >60 m yrˉ1 in the debris-free accumulation area. The type-II glaciers exhibit active tongues (>50 m yrˉ1) yet have slow movement in the accumulation zone. The type-III glaciers show prolonged (<10 m yrˉ1) yet consistent movement throughout the flow line. Results show that the average surface velocity of studied glaciers was 11.10 ± 4.1 m yrˉ1 in 1992/93, which increased (by ~43%) to 15.87 ± 2.4 m yrˉ1 in 2000/02 and further increased (by ~59%) to 25.25 ± 1.5 m yrˉ1 in 2017/18. Glaciers show seasonal fluctuations in surface velocities with an apparent “summer speedup” of ~19%–200% compared to the winter velocities. Inter-annual velocities show an increasing trend during the observation periods. Analysis of NCEP/NCAR gridded data also reveals that the temperature increased by 0.55 °C while precipitation decreased by 0.73 mm during 1948–2018.Our results indicate that glaciers remain dynamic throughout their length with systematic spatiotemporal variations in surface velocity that points towards the control of several topographical and morphological factors. The spatially heterogeneous pattern in surface velocity is characterized by zones of high activity crevasses with steep gradients (>30°) showing maximum ice movement at higher elevations, while debris-covered tongues in the low elevations having gentle slopes (<2°) are nearly stagnant. Based on our results and evidences from the literatures, we suggest that seasonal variations (i.e., summer speedup) in surface velocity in the JCW are due to seasonal temperature fluctuations that alter meltwater availability to the subglacial processes akin to the other Himalaya glaciers. An increasing trend in annual velocity manifests the rising trend in temperature in the western Himalaya. Local topographic configuration, combined with regional climatic systems, controls the amount and types of precipitation received in areas like ours to sustain glaciers on a millennial-scale.

Application of Sentinel-1 and-2 Images in Measuring the Deformation of Kuh-e-Namak (Dashti) Namakier, Iran

Kuh-e-Namak (Dashti) namakier is one of the most active salt diapirs along the Zagros fold–thrust belt in Iran. Its surface deformation should be measured to estimate its long-term kinematics. Ten Sentinel-2 optical images acquired between October 2016 and December 2019 were processed by using Co-Registration of Optically Sensed Images and Correlation (COSI-Corr) method. Forty-seven Sentinel-1 ascending Synthetic Aperture Radar (SAR) images acquired between April 2017 and December 2019 were processed by using Small Baseline Subset Synthetic Aperture Radar Interferometry (SBAS-InSAR) method. The deformation of Kuh-e-Namak (Dashti) namakier was measured using both methods. Then, meteorological data were utilized to explore the relationship between the kinematics of the namakier and weather conditions and differences in macrodeformation behavior of various rock salt types. The advantages and disadvantages of COSI-Corr and SBAS-InSAR methods in measuring the deformation of the namakier were compared. The results show that: (1) The flank subsides in the dry season and uplifts in the rainy season, whereas the dome subsides in the rainy season and uplifts in the dry season. Under extreme rainfall conditions, the namakier experiences permanent plastic deformation. (2) The “dirty” rock salt of the namakier is more prone to flow than the “clean” rock salt in terms of macrodeformation behavior. (3) In the exploration of the kinematics of the namakier via the two methods, COSI-Corr is superior to SBAS-InSAR on a spatial scale, but the latter is superior to the former on a time scale.

Spatiotemporal Variability of Velocity and Influence of Glacier Thickness Using Landsat Imagery: Hunza River Basin, Karakoram Range

The Karakoram Anomaly has been intensively investigated, but the factors that control this anomaly, such as the glacier velocity, topography, and mass balance, remain poorly understood. To improve our understanding of the velocity, topography, and mass balance of the Karakoram Glacier, in this study, the spatiotemporal variability of four glacier velocities in the Hunza Basin of the Karakoram range were surveyed using co-registration of optically sensed images and correlation (COSI-Corr) on Landsat imagery from 1993–2019. The results show that the velocity of the Gulmit Glacier increases with a rising altitude from the glacier terminal. The three other glaciers initially display high velocity, followed by a decrease from the glacier terminal, with the maximum velocity attained in the middle of the glacier. In addition, the Karakoram glaciers produced a slight mass gain, with all mountain glaciers exhibiting clear regional acceleration from 1993–2019. The ice deformation velocity of the Batura Glacier diminished at an average rate of 8.49 %. However, the topography of the glacier base and physical factors require further analysis to determine their contribution to the observed changes in glacier velocity. In the present work, multi-temporal remote sensing image interpretations were carried out to determine glacier kinematics, which could enhance our understanding of glacier change mechanisms.

Selecting the Best Image Pairs to Measure Slope Deformation

Optical remote sensing images can be used to monitor slope deformation in mountain regions. Abundant optical sensors onboard various platforms were designed to provide increasingly high spatial–temporal resolution images at low cost; however, finding the best image pairs to derive slope deformation remains difficult. By selecting a location in the east Tibetan Plateau, this work used the co-registration of optically sensed images and correlation (COSI-Corr) method to analyze 402 Sentinel-2 images from August 2015 to February 2020, to quantify temporal patterns of uncertainty in deriving slope deformation. By excluding 66% of the Sentinel-2 images that were contaminated by unfavorable weather, uncertainties were found to fluctuate annually, with the least uncertainty achieved in image pairs of similar dates in different years. Six image pairs with the least uncertainties were selected to derive ground displacement for a moving slope in the study area. Cross-checks among these image pairs showed consistent results, with uncertainties less than 1/10 pixels in length. The findings from this work could help in the selection of the best image pairs to derive reliable slope displacement from large numbers of optical images.

Long-Term Analysis of Sea Ice Drift in the Western Ross Sea, Antarctica, at High and Low Spatial Resolution

The Ross Sea region, including three main polynya areas in McMurdo Sound, Terra Nova Bay, and in front of the Ross Ice Shelf, has experienced a significant increase in sea ice extent in the first four decades of satellite observations. Here, we use Co-Registration of Optically Sensed Images and Correlation (COSI-Corr) to estimate 894 high-resolution sea ice motion fields of the Western Ross Sea in order to explore ice-atmosphere interactions based on sequential high-resolution Advanced Synthetic Aperture Radar (ASAR) images from the Envisat satellite acquired between 2002–2012. Validation of output motion vectors with manually drawn vectors for 24 image pairs show Pearson correlation coefficients of 0.92 ± 0.09 with a mean deviation in direction of −3.17 ± 6.48 degrees. The high-resolution vectors were also validated against the Environment and Climate Change Canada sea ice motion tracking algorithm, resulting in correlation coefficients of 0.84 ± 0.20 and the mean deviation in the direction of −0.04 ± 17.39 degrees. A total of 480 one-day separated velocity vector fields have been compared to an available NSIDC low-resolution sea ice motion vector product, showing much lower correlations and high directional differences. The high-resolution product is able to better identify short-term and spatial variations, whereas the low-resolution product underestimates the actual sea ice velocities by 47% in this important near-coastal region. The large-scale pattern of sea ice drift over the full time period is similar in both products. Improved image coverage is still desired to capture drift variations shorter than 24 h.

Spatio-temporal trends in the surface ice velocities of the central Himalayan glaciers, India

The glacier surface ice velocity (SIV) is important in understanding the glacier state. This study presents results on the SIV of the 18 glaciers spread over the Indian central Himalaya (ICH). The SIV was computed by applying Co-registration of Optically Sensed Images and Correlation (COSI-Corr) technique on the Landsat time series data (1993–2017). Results show that the average SIV of all glaciers was 22.63 ± 5.8 m a −1 in 1993/94, which decreased (by ~23%) to 17.32 ± 3.1 m a −1 in 2000/01 and further declined (by ~33%) to 11.50 ± 1.7 m a −1 in 2015/16. Though a secular decline in average SIV is observed, rates of slowdown are considerably heterogeneous for the studied glaciers being largely determined by glaciers size, orientation, altitude and debris cover. Slope was found to have comparatively low influence on the glacier movement. Inter-regional comparison reveals that average SIVs of the ICH glaciers were slightly but consistently lower than that of the western and eastern Himalayan glaciers. Nonetheless, though moving slowly, ICH glaciers are more active than nearby Everest region glaciers with sufficient proportion of active glaciers (referred as Type-I; 39%). However, the point of concern is that owing to declining health, ICH-glaciers are progressively converting from Type-I to partially active (referred as Type-II), and Type-II to entirely stagnant (referred as Type-III). This observed slowdown coupled with negative mass balance and continuous debris growth (as reported in previous studies) may form favorable conditions for supraglacial lake development. We thereby recommend regular monitoring of glacier dynamics in this region for tenable assessment of climatic change impacts. • Velocities for 18 central Himalayan glaciers have been estimated between 1990 and 2015. • All the studied glaciers have significantly slowed-down during ~1990–2015. • Central Himalayan glaciers moved slowly than western and central Himalaya. • Entirely active glaciers have progressively been converted into entirely stagnant glaciers. • Glacier’ size, orientation, altitude and debris cover determine movement heterogeneity.

Retrospective deformation of the Baige landslide using optical remote sensing images

Detecting slope deformations before major landslides is crucially important for mitigating landslide disasters. In this work, we explored the use of Sentinel-2 images and an image correlation method, Co-Registration of Optically Sensed Images and Correlation (COSI-Corr), to derive slope deformations before the 2018 Baige landslide along the Jinsha River. We found that larger sliding windows outperform smaller ones in extracting the moving slope. Different solar zenith angles in image pairs have an influence on the derived displacements. Although the spatial resolution of Sentinel-2 images is 10 m, uncertainties in estimating slope deformation are found within 2 m. Using the COSI-Corr technique, we monitored sub-pixel slope deformation in Sentinel-2 images from November 2015 to August 2018. We found that the slope moved faster in summer than in winter months, which was probably driven by the monsoon climate in this region. From 2015 to 2018, the slope movement became faster, and an acceleration stage was observed before the slope failed completely. To derive reliable slope displacements, this work suggests testing different sliding window size combinations in the use of image correlation methods, and optical images acquired with similar zenith angles are preferred. This work also demonstrated the capability of using optical remote sensing images to monitor large slope deformations before major landslides. As more optical images with high spatial resolution become available, monitoring minor slope deformations directly would be practicable for large remote mountain regions.

Evidence of Instability in Previously-Mapped Landslides as Measured Using GPS, Optical, and SAR Data between 2007 and 2017: A Case Study in the Portuguese Bend Landslide Complex, California

Velocity dictates the destructive potential of a landslide. A combination of synthetic aperture radar (SAR), optical, and GPS data were used to maximize spatial and temporal coverage to monitor continuously-moving portions of the Portuguese Bend landslide complex on the Palos Verdes Peninsula in Southern California. Forty SAR images from the COSMO-SkyMed satellite, acquired between 19 July 2012 and 27 September 2014, were processed using Persistent Scatterer Interferometry (PSI). Eight optical images from the WorldView-2 satellite, acquired between 20 February 2011 and 16 February 2016, were processed using the Co-registration of Optically Sensed Images and Correlation (COSI-Corr) technique. Displacement measurements were taken at GPS monuments between September 2007 and May 2017. Incremental and average deformations across the landslide complex were measured using all three techniques. Velocity measured within the landslide complex ranges from slow (&gt; 1.6 m/year) to extremely slow (&lt; 16 mm/year). COSI-Corr and GPS provide detailed coverage of m/year-scale deformation while PSI can measure extremely slow deformation rates (mm/year-scale), which COSI-Corr and GPS cannot do reliably. This case study demonstrates the applicability of SAR, optical, and GPS data synthesis as a complimentary approach to repeat field monitoring and mapping to changes in landslide activity through time.

Assessment of glacier stored water in Karakoram Himalaya using satellite remote sensing and field investigation

Karakoram Himalaya (KH) has continental climatic conditions and possesses largest concentration of glaciers outside the polar regions. The melt water from these glaciers is a major contributor to the Indus river. In this study, various methods have been used to estimate the ice volume in the Karakoram Range of glaciers such as Co-registration of Optically Sensed Images and Correlation (COSI-Corr) method and Area-Volume relations. Landsat 8 satellite data has been used to generate the ice displacement, velocity and thickness map. Our study for 558 Karakoram glaciers revealed that the average ice thickness in Karakoram is 90 m. Ground Penetrating Radar (GPR) survey has been conducted in one of the KH glacier i.e. Saser La glacier and the collected GPR data is used for the validation of satellite derived thickness map. GPR measured glacier thickness values are found comparable with satellite estimated values with RMSE of 4.3 m. The total ice volume of the Karakoram glaciers is estimated to be 1607±19 km3(1473±17 Gt), which is equivalent to 1473±17 km3 of water equivalent. Present study also covers the analysis of glacier surface displacement, velocity and ice thickness values with reference to glacier mean slope.

The Search for Active Marsquakes Using Subpixel Coregistration and Correlation: Best Practice and First Results

AbstractThe state of seismic activity on Mars is currently unknown. On Earth, coseismic displacement has been observed using visible wavelength images and subpixel coregistration and correlation techniques. We apply this method to Mars with the COSI‐Corr (Co‐registration of Optically Sensed Images and Correlation) software package using High‐Resolution Imaging Science Experiment (HiRISE) images, focusing on part of the Cerberus Fossae fault system. We derive best practices for applying this method to the study of coseismic displacements on Mars. Using a time series of eight overlapping HiRISE images, we achieve pixel coregistration with a mean accuracy of about 1/50 of a pixel. We see no clear evidence for coseismic displacement in this region during a time period of over 8 years. One possible displacement signal (1–2 m of west‐east displacement over a length scale of about 50 m) that has similarities to terrestrial coseismic deformation was dismissed as the result of incomplete correction of steep topography during the coregistration stage. Ancillary observations of recurring slope lineae (RSL) activity in the surrounding fault system offer no supporting evidence for the occurrence of coseismic displacement but do seem to suggest RSL activity that does not fit into previous seasonal timescales. Although it is unlikely that we have observed coseismic displacement in our study area during this time period, the best practice method and the accuracy of our results offer encouragement for future studies. HiRISE, Context Camera, and Color and Stereo Surface Imaging System images can be used to complement and independently verify in situ seismic observations by the InSight (Interior Exploration using Seismic Investigations, Geodesy, and Heat Transport) lander or source location changes from the ExoMars Trace Gas Orbiter spacecraft.

Temporal Change and Flow Velocity Estimation of Patseo Glacier, Western Himalaya, India

In the present study we estimate the velocity and thickness of the Patseo glacier, Himachal Pradesh, India. The average velocity of the glacier was estimated as similar to 5.47 m/year using co-registration of optically sensed images and correlation (COSI-Corr) method. The glacier thickness was found to vary between 12 and 278 m, with an average value 59 m. The total glacier ice volume was estimated as similar to 15.8 x 10(7) m(3), with equivalent water reservoir of similar to 14.5 x 10(7) m(3). Ground penetrating radar (GPR) surveys were conducted during 2004 and 2013 for validation of the estimated glacier thickness. The glacier thickness estimated using COSI-Corr method was found to be in agreement with GPR-retrieved glacier thickness (RMSE = 4.75 m; MAE = 3.74 m). The GPR profiles collected along the same geographic locations on the glacier during 2004 and 2013 showed a reduction in ice thickness of similar to 1.89 m, and thus resulting in an annual ice thickness decrease of similar to 0.21 m. The glacier area was estimated for 2004 and 2013 using LISS IV satellite data and found to be similar to 2.52 and similar to 2.30 sq. km respectively. This shows an annual reduction of similar to 0.024 sq. km in glacier area. The total annual loss in glacier ice volume was estimated as similar to 4.55 x 10(5) m(3). This loss in the glacier ice volume of the Patseo glacier is supported by the snow and meteorological observations collected at a nearby field observatory of Snow and Avalanche Study Establishment (SASE). The climate data collected at SASE meteorological observatory at Patseo (3800 m), between 1993-94 and 2014-15 showed an increasing trend in the mean annual temperature and a decreasing trend in winter precipitation.

Estimation of dune migration rates north Riyadh City, KSA, using SPOT 4 panchromatic images

Irq Al-Rethmah is located north of Riyadh City, KSA, as elongated NW-SE sand accumulations. Its formation and development are highly controlled by the ridge-and-valley landscape dominant in the east of Saudi Arabia. The active dunes of Irq Al-Rethmah are basically represented by barchan and transverse dunes. These active dunes either superimpose the old stable dunes and sand sheets or directly occur over the alluvial plain adjacent to the western reaches of old stable dunes. The Co-registration of optically sensed images and Correlation (COSI-Corr) technology was conducted on two SPOT 4 panchromatic images acquired in 2006 and 2009 respectively to determine the migration rates and direction of the active dunes. The average annual migration rates of active dunes ranged from 1.6 to 2.25 m/yr. The migration rates decrease where the active dunes superimpose the old stable dunes and sand sheets. On the other hand, these rates increase when the active dunes are located over the alluvial plain along the western margins of Irq Al-Rethmah. The calculated vector displacement field by COSI-Corr technology suggest a southward direction of dune migration indicating that the predominant wind direction is northerly. Although the calculated rates are generally low in comparison to other measured migration rates of sand dunes in the east of Saudi Arabia, the spatial analysis implies potential hazards of active dunes against many landuse components such as roads, powerlines, and recreational facilities in the study area.

Remote sensing flow velocity of debris-covered glaciers using Landsat 8 data

Changes in ice velocity of a glacier regulate its mass balance and dynamics. The estimation of glacier flow velocity is therefore an important aspect of temporal glacier monitoring. The utilisation of conventional ground-based techniques for detecting glacier surface flow velocity in the rugged and alpine Himalayan terrain is extremely difficult. Remote sensing-based techniques can provide such observations on a regular basis for a large geographical area. Obtaining freely available high quality remote sensing data for the Himalayan regions is challenging. In the present work, we adopted a differential band composite approach, for the first time, in order to estimate glacier surface velocity for non-debris and supraglacial debris covered areas of a glacier, separately. We employed various bandwidths of the Landsat 8 data for velocity estimation using the COSI-Corr (co-registration of optically sensed images and correlation) tool. We performed the accuracy assessment with respect to field measurements for two glaciers in the Indian Himalaya. The panchromatic band worked best for non-debris parts of the glaciers while band 6 (SWIR – short wave infrared) performed best in case of debris cover. We correlated six temporal Landsat 8 scenes in order to ensure the performance of the proposed algorithm on monthly as well as yearly timescales. We identified sources of error and generated a final velocity map along with the flow lines. Over- and underestimates of the yearly glacier velocity were found to be more in the case of slow moving areas with annual displacements less than 5 m. Landsat 8 has great capabilities for such velocity estimation work for a large geographic extent because of its global coverage, improved spectral and radiometric resolutions, free availability and considerable revisit time.

The application of COSI‐Corr to determine dune system dynamics in the southern Namib Desert using ASTER data

ABSTRACTThe Coregistration of Optically Sensed Images and Correlation (COSI‐Corr) algorithm was used to estimate dune migration and sand flux rates from a series of remotely‐sensed optical image pairs. Several areas of barchan and transverse dunes transport sand along definite pathways, feeding the southern part of the Namib Sand Sea from beaches and deflationary basins in the Sperrgebiet. We give a detailed description of the pre‐ and post‐processing routines used for our COSI‐Corr analysis, and we evaluate the sub‐pixel dune migration results at the dune and dune‐field scales. The best set of parameters for the application of the algorithm was systematically derived, resulting in methodological refinements of the cross‐correlation windows. The Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) sensor aboard the Terra satellite provided the remote sensing imagery. Few comparisons have been made between dune migration measurements using COSI‐Corr and other types of change detection analysis, and few dune fields have served as test cases for COSI‐Corr. We suggest that analysis and interpretation of COSI‐Corr output from ASTER data is more valuable if combined with other image analysis techniques, such as manual digitization of dunes in a geographic information system (GIS), processing of write memory function insertion (WMFI) imagery and multispectral image (MSI) analysis of composition. The dune migrations estimated from COSI‐Corr results were validated using GIS and WMFI, and later MSI analysis added an important regional, contextual framework of sand transport pathways. The synthesis of these works lends more confidence to understanding the Namib dune system's dynamics and provides a basis for future comparisons to other dune fields. Copyright © 2013 John Wiley &amp; Sons, Ltd.

Retrieving sand dune movements using sub-pixel correlation of multi-temporal optical remote sensing imagery, northwest Sinai Peninsula, Egypt

Sand dune movements pose potential hazards against various land use activities in Egypt. To avoid or to minimize the hazards associated with sand dunes, it is critical to determine their rates and patterns of migration at high accuracy and over wide spatial coverage. This is, however, a real challenge using field work and traditional remote sensing approaches. The co-registration of optically sensed images and correlation (COSI-Corr) complements traditional approaches to provide accurate measurements at wide spatial coverage. Applying the COSI-Corr technique to two SPOT 4 panchromatic images acquired above North Sinai, we measured lateral migration of 6.0 to 19.4m/yr with an average of 7.7m/yr, and 9.3 to 15.0m/yr with an average of 11.9m/yr for the whole barchans dune areas and a selected sample of barchan dunes, respectively. We also detected that the lateral movements along the crest lines of linear dunes ranged from 4.0 to 20.1m/yr with an average of 6.8m/yr for the whole area occupied by linear dunes. For a selected linear dune within the study area, the lateral migration of peaks and saddles along the crest lines ranged from 5.5 to 16.7m/yr with an average of 12.4m/yr. The lateral migration of both barchans dunes and linear dunes showed high spatial variability. Validation of these results against the previously measured migration rates indicated high degree of accuracy of the technique. In addition, the displacement field produced from the correlation indicated that the direction of sand dune movements occurred towards the east and southeast, which is well aligned with the previously determined sand dune drifting potentials.

In-Flight CCD Distortion Calibration for Pushbroom Satellites Based on Subpixel Correlation

We describe a method that allows for accurate inflight calibration of the interior orientation of any pushbroom camera and that in particular solves the problem of modeling the distortions induced by charge coupled device (CCD) misalignments. The distortion induced on the ground by each CCD is measured using subpixel correlation between the orthorectified image to be calibrated and an orthorectified reference image that is assumed distortion free. Distortions are modeled as camera defects, which are assumed constant over time. Our results show that in-flight interior orientation calibration reduces internal camera biases by one order of magnitude. In particular, we fully characterize and model the Satellite Pour l'Observation de la Terre (SPOT) 4-HRV1 sensor, and we conjecture that distortions mostly result from the mechanical strain produced when the satellite was launched rather than from effects of on-orbit thermal variations or aging. The derived calibration models have been integrated to the software package Coregistration of Optically Sensed Images and Correlation (COSI-Corr), freely available from the Caltech Tectonics Observatory website. Such calibration models are particularly useful in reducing biases in digital elevation models (DEMs) generated from stereo matching and in improving the accuracy of change detection algorithms.