scholarly journals Validation of ICESat-2 ATLAS Bathymetry and Analysis of ATLAS’s Bathymetric Mapping Performance

2019 ◽  
Vol 11 (14) ◽  
pp. 1634 ◽  
Author(s):  
Christopher E. Parrish ◽  
Lori A. Magruder ◽  
Amy L. Neuenschwander ◽  
Nicholas Forfinski-Sarkozi ◽  
Michael Alonzo ◽  
...  
Keyword(s):  
Infrared Imaging ◽  
Photon Counting ◽  
Water Clarity ◽  
Virgin Islands ◽  
Maximum Depth ◽  
Laser Altimeter ◽  
Bathymetric Mapping ◽  
Primary Focus ◽  
Using Data ◽  
Water Depths

NASA’s Ice, Cloud, and Land Elevation Satellite-2 (ICESat-2) was launched in September, 2018. The satellite carries a single instrument, ATLAS (Advanced Topographic Laser Altimeter System), a green wavelength, photon-counting lidar, enabling global measurement and monitoring of elevation with a primary focus on the cryosphere. Although bathymetric mapping was not one of the design goals for ATLAS, pre-launch work by our research team showed the potential to map bathymetry with ICESat-2, using data from MABEL (Multiple Altimeter Beam Experimental Lidar), NASA’s high-altitude airborne ATLAS emulator, and adapting the laser-radar equation for ATLAS specific parameters. However, many of the sensor variables were only approximations, which limited a full assessment of the bathymetric mapping capabilities of ICESat-2 during pre-launch studies. Following the successful launch, preliminary analyses of the geolocated photon returns have been conducted for a number of coastal sites, revealing several salient examples of seafloor detection in water depths of up to ~40 m. The geolocated seafloor photon returns cannot be taken as bathymetric measurements, however, since the algorithm used to generate them is not designed to account for the refraction that occurs at the air–water interface or the corresponding change in the speed of light in the water column. This paper presents the first early on-orbit validation of ICESat-2 bathymetry and quantification of the bathymetric mapping performance of ATLAS using data acquired over St. Thomas, U.S. Virgin Islands. A refraction correction, developed and tested in this work, is applied, after which the ICESat-2 bathymetry is compared against high-accuracy airborne topo-bathymetric lidar reference data collected by the U.S. Geological Survey (USGS) and the National Oceanic and Atmospheric Administration (NOAA). The results show agreement to within 0.43—0.60 m root mean square error (RMSE) over 1 m grid resolution for these early on-orbit data. Refraction-corrected bottom return photons are then inspected for four coastal locations around the globe in relation to Visible Infrared Imaging Radiometer Suite (VIIRS) Kd(490) data to empirically determine the maximum depth mapping capability of ATLAS as a function of water clarity. It is demonstrated that ATLAS has a maximum depth mapping capability of nearly 1 Secchi in depth for water depths up to 38 m and Kd(490) in the range of 0.05–0.12 m−1. Collectively, these results indicate the great potential for bathymetric mapping with ICESat-2, offering a promising new tool to assist in filling the global void in nearshore bathymetry.

A Digital Terrain Modeling Method in Urban Areas by the ICESat-2 (Generating precise terrain surface profiles from photon-counting technology)

2021 ◽  
Vol 87 (4) ◽  
pp. 237-248
Author(s):  
Nahed Osama ◽  
Bisheng Yang ◽  
Yue Ma ◽  
Mohamed Freeshah
Keyword(s):  
Urban Areas ◽  
Spatial Clustering ◽  
Photon Counting ◽  
Ground Surface ◽  
Ground Truth ◽  
Surface Model ◽  
Laser Altimeter ◽  
Ground Truth Data ◽  
Urban Scenes ◽  
Terrain Surface

The ICE, Cloud and land Elevation Satellite-2 (ICES at-2) can provide new measurements of the Earth's elevations through photon-counting technology. Most research has focused on extracting the ground and the canopy photons in vegetated areas. Yet the extraction of the ground photons from urban areas, where the vegetation is mixed with artificial constructions, has not been fully investigated. This article proposes a new method to estimate the ground surface elevations in urban areas. The ICES at-2 signal photons were detected by the improved Density-Based Spatial Clustering of Applications with Noise algorithm and the Advanced Topographic Laser Altimeter System algorithm. The Advanced Land Observing Satellite-1 PALSAR –derived digital surface model has been utilized to separate the terrain surface from the ICES at-2 data. A set of ground-truth data was used to evaluate the accuracy of these two methods, and the achieved accuracy was up to 2.7 cm, which makes our method effective and accurate in determining the ground elevation in urban scenes.

scholarly journals Towards a Miniaturized Photon Counting Laser Altimeter and Stereoscopic Camera Instrument Suite for Microsatellites

2009 ◽  
pp. 341-350
Author(s):  
S.G. Moon ◽  
S. Hannemann ◽  
M. Collon ◽  
K. Wielinga ◽  
E. Kroesbergen ◽  
...  
Keyword(s):  
Photon Counting ◽  
Laser Altimeter

scholarly journals Land ice height-retrieval algorithm for NASA's ICESat-2 photon-counting laser altimeter

2019 ◽  
Vol 233 ◽  
pp. 111352 ◽  
Author(s):  
Benjamin Smith ◽  
Helen A. Fricker ◽  
Nicholas Holschuh ◽  
Alex S. Gardner ◽  
Susheel Adusumilli ◽  
...  
Keyword(s):  
Photon Counting ◽  
Retrieval Algorithm ◽  
Laser Altimeter

The Solar System Treks Mosaic Pipeline (SSTMP)

2020 ◽  
Author(s):  
Aaron Curtis ◽  
Emily Law ◽  
Shan Malhotra ◽  
Brian Day ◽  
Marshall Trautman ◽  
...  
Keyword(s):  
Solar System ◽  
Open Source ◽  
Laser Altimeter ◽  
Narrow Angle ◽  
Spatial Alignment ◽  
Stereo Reconstruction ◽  
Common Framework ◽  
Mosaic Generation ◽  
Using Data ◽  
Processing Steps

<p>Solar System Treks Mosaic Pipeline (SSTMP) is a new, open-source tool for generation of planetary DEM and orthoimage mosaics. Opportunistic stereo reconstruction from pre-existing orbital imagery has in the past typically required significant human input, particularly in the pair selection and spatial alignment steps. Previous stereo mosaics incorporate myriad human decisions, compromising the reproducibility of the process and complicating uncertainty analysis. Lack of a common framework for recording operator input has hindered the community's ability to collaborate and share experience to improve stereo reconstruction techniques. SSTMP provides a repeatable, turnkey, end-to-end solution for creating these products. The user requests mosaic generation for a bounding box or polygon, initiating a workflow which results in deliverable mosaics usable for site characterization, science, and public outreach.</p> <p>The inital release of SSTMP focuses on production of elevation and orthoimage mosaics using data from the Lunar Reconaissance Orbiter's Narrow Angle Camera (LRO NAC). SSTMP can automatically select viable stereo pairs, complete stereo reconstruction, refine alignments using data from the LRO's laser altimeter (LOLA), and combine the data to produce orthoimage, elevation, and color hillshade mosaics.</p> <p>SSTMP encapsulates the entire stereo mosaic production process into one workflow, managed by Argo Workflow opensource Kubernetes-based software. Each process runs in a container including all tools necessary for production and geospatial analysis of mosaics, ensuring a consistent computing environment. SSTMP automatically retrieves all necessary data. For processing steps, it leverages free and open-source software including Ames Stereo Pipeline, USGS ISIS, Geopandas, GDAL, and Orfeo toolbox.</p>

scholarly journals Land-ice elevation changes from photon-counting swath altimetry: first applications over the Antarctic ice sheet

2015 ◽  
Vol 61 (225) ◽  
pp. 17-28 ◽  
Author(s):  
Duncan A. Young ◽  
Laura E. Lindzey ◽  
Donald D. Blankenship ◽  
Jamin S. Greenbaum ◽  
Alvaro Garcia De Gorordo ◽  
...  
Keyword(s):  
Dynamic Change ◽  
High Surface ◽  
Photon Counting ◽  
Ice Sheet ◽  
Test Case ◽  
Laser Altimeter ◽  
Surface Slopes ◽  
Elevation Changes ◽  
The Alamo ◽  
Cross Track

AbstractSatellite altimetric time series allow high-precision monitoring of ice-sheet mass balance. Understanding elevation changes in these regions is important because outlet glaciers along ice-sheet margins are critical in controlling flow of inland ice. Here we discuss a new airborne altimetry dataset collected as part of the ICECAP (International Collaborative Exploration of the Cryosphere by Airborne Profiling) project over East Antarctica. Using the ALAMO (Airborne Laser Altimeter with Mapping Optics) system of a scanning photon-counting lidar combined with a laser altimeter, we extend the 2003–09 surface elevation record of NASA’s ICESat satellite, by determining cross-track slope and thus independently correcting for ICESat’s cross-track pointing errors. In areas of high slope, cross-track errors result in measured elevation change that combines surface slope and the actual Δz/Δt signal. Slope corrections are particularly important in coastal ice streams, which often exhibit both rapidly changing elevations and high surface slopes. As a test case (assuming that surface slopes do not change significantly) we observe a lack of ice dynamic change at Cook Ice Shelf, while significant thinning occurred at Totten and Denman Glaciers during 2003–09.

scholarly journals SARS-CoV-2 Infection Fatality Rates in India: Systematic Review, Meta-analysis and Model-based Estimation

2021 ◽  
pp. 232102222110543
Author(s):  
Lauren Zimmermann ◽  
Subarna Bhattacharya ◽  
Soumik Purkayastha ◽  
Ritoban Kundu ◽  
Ritwik Bhaduri ◽  
...  
Keyword(s):  
Meta Analysis ◽  
Case Fatality ◽  
Fatality Rate ◽  
Excess Death ◽  
Seir Model ◽  
Model Based ◽  
Quantitative Synthesis ◽  
Primary Focus ◽  
Using Data ◽  
Excess Deaths

Introduction: Fervourous investigation and dialogue surrounding the true number of SARS-CoV-2-related deaths and implied infection fatality rates in India have been ongoing throughout the pandemic, and especially pronounced during the nation’s devastating second wave. We aim to synthesize the existing literature on the true SARS-CoV-2 excess deaths and infection fatality rates (IFR) in India through a systematic search followed by viable meta-analysis. We then provide updated epidemiological model-based estimates of the wave 1, wave 2 and combined IFRs using an extension of the Susceptible-Exposed-Infected-Removed (SEIR) model, using data from 1 April 2020 to 30 June 2021. Methods: Following PRISMA guidelines, the databases PubMed, Embase, Global Index Medicus, as well as BioRxiv, MedRxiv and SSRN for preprints (accessed through iSearch), were searched on 3 July 2021 (with results verified through 15 August 2021). Altogether, using a two-step approach, 4,765 initial citations were screened, resulting in 37 citations included in the narrative review and 19 studies with 41datapoints included in the quantitative synthesis. Using a random effects model with DerSimonian-Laird estimation, we meta-analysed IFR1, which is defined as the ratio of the total number of observed reported deaths divided by the total number of estimated infections, and IFR2 (which accounts for death underreporting in the numerator of IFR1). For the latter, we provided lower and upper bounds based on the available range of estimates of death undercounting, often arising from an excess death calculation. The primary focus is to estimate pooled nationwide estimates of IFRs with the secondary goal of estimating pooled regional and state-specific estimates for SARS-CoV-2-related IFRs in India. We also tried to stratify our empirical results across the first and second waves. In tandem, we presented updated SEIR model estimates of IFRs for waves 1, 2, and combined across the waves with observed case and death count data from 1 April 2020 to 30 June 2021. Results: For India, countrywide, the underreporting factors (URF) for cases (sourced from serosurveys) range from 14.3 to 29.1 in the four nationwide serosurveys; URFs for deaths (sourced from excess deaths reports) range from 4.4 to 11.9 with cumulative excess deaths ranging from 1.79 to 4.9 million (as of June 2021). Nationwide pooled IFR1 and IFR2 estimates for India are 0.097% (95% confidence interval [CI]: 0.067–0.140) and 0.365% (95% CI: 0.264–0.504) to 0.485% (95% CI: 0.344–0.685), respectively, again noting that IFR2 changes as excess deaths estimates vary. Among the included studies in this meta-analysis, IFR1 generally appears to decrease over time from the earliest study end date to the latest study end date (from 4 June 2020 to 6 July 2021, IFR1 changed from 0.199 to 0.055%), whereas a similar trend is not as readily evident for IFR2 due to the wide variation in excess death estimates (from 4 June 2020 to 6 July 2021, IFR2 ranged from (0.290–1.316) to (0.241–0.651)%). Nationwide SEIR model-based combined estimates for IFR1 and IFR2 are 0.101% (95% CI: 0.097–0.116) and 0.367% (95% CI: 0.358–0.383), respectively, which largely reconcile with the empirical findings and concur with the lower end of the excess death estimates. An advantage of such epidemiological models is the ability to produce daily estimates with updated data, with the disadvantage being that these estimates are subject to numerous assumptions, arduousness of validation and not directly using the available excess death data. Whether one uses empirical data or model-based estimation, it is evident that IFR2 is at least 3.6 times more than IFR1. Conclusion: When incorporating case and death underreporting, the meta-analysed cumulative infection fatality rate in India varied from 0.36 to 0.48%, with a case underreporting factor ranging from 25 to 30 and a death underreporting factor ranging from 4 to 12. This implies, by 30 June 2021, India may have seen nearly 900 million infections and 1.7–4.9 million deaths when the reported numbers stood at 30.4 million cases and 412 thousand deaths (Coronavirus in India) with an observed case fatality rate (CFR) of 1.35%. We reiterate the need for timely and disaggregated infection and fatality data to examine the burden of the virus by age and other demographics. Large degrees of nationwide and state-specific death undercounting reinforce the call to improve death reporting within India. JEL Classifications: I15, I18

Comparison of the Uzboi Vallis and Nirgal Vallis (Mars) using swath analysis

2021 ◽  
Author(s):  
András Szilágyi-Sándor ◽  
Balázs Székely
Keyword(s):  
Profile Analysis ◽  
River System ◽  
Analysis Method ◽  
Impact Cratering ◽  
Laser Altimeter ◽  
Terrain Models ◽  
Half Graben ◽  
Using Data ◽  
Morava River ◽  
Near Future

<p>The presumably fluvially affected surfaces of Mars provide evidence of the variety of surface processes of the past of the planet. Throughout its history, the climate has enabled the presence of liquid water several times (perhaps periodically). Watercourses and mega-river systems have ruled the surface; their tracks are still recognizable in many places. The Argyre Crater might have served as the source of such a huge river system: the Uzboi–Ladon–Morava River System (ULM), during the Late Noachian. (Dohm et al 2015) ULM is therefore fundamentally different from most of the valleys and channels of Mars as it is not an amphitheatre-headed valley, it is composed of various types of sections, and its source is connected to a large crater. In this study Uzboi Vallis, a section of ULM was studied using data from the Mars Global Surveyor's Mars Orbiter Laser Altimeter (MOLA) data. A comparison is presented of Uzboi Vallis and its tributary, Nirgal Vallis. In addition to creating the stream orders of the valleys and traditional elevation profiles, we used the swath profile analysis method. The swath analysis is fundamentally different from elevation profiles that enhance the specific Martian conditions (impact cratering, the complete absence of the biosphere, less gravity). In addition to the swath analysis completely covering the two studied areas, several regions of the catchment were specifically analyzed. According to the results obtained, the Uzboi Vallis is at least partly tectonically modified. Based on these observations, in the northeastern part, half-graben structures are hypothesized. The method of swath profile analysis, previously not applied to Martian data, proved to be useful and provided interpretable data for the surface of a planet other than Earth.</p><p>Geomorphometric studies on terrain models are found to provide interesting information paving the way towards an in-depth understanding of this mega river system. Further analysis of the ULM is planned in the near future.</p><p>Dohm, J.M., Hare, T.M., Robbins, S.J., Williams, J.-P., Soare, R.J., El-Maarry, M.R., Conway, S.J., Buczkowski, D.L., Kargel, J.S., Banks, M.E., Fairén, A.G., Schulze-Makuch, D., Komatsu, G., Miyamoto, H., Anderson, R.C., Davila, A.F., Mahaney, W.C., Fink, W., Cleaves, H.J., Yan, J., Hynek, B., Maruyama, S. (2015): Geological and hydrological histories of the Argyre province, Mars. Icarus 253:66–98.</p>

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