scholarly journals TEMPORAL STABILITY OF TUZ GÖLÜ AND ATACAMA DESERT REFERENCE SURFACES FOR ABSOLUTE CALIBRATION OF ORBITAL SENSORS

2015 ◽  
Vol 33 (2) ◽  
Author(s):  
Cibele Teixeira Pinto ◽  
Flávio Jorge Ponzoni ◽  
Ruy Morgado Castro
Keyword(s):  
Optical Sensors ◽  
Temporal Stability ◽  
Atacama Desert ◽  
Temporal Analysis ◽  
Earth Observation ◽  
Sensor Calibration ◽  
Absolute Calibration ◽  
Radiometric Calibration ◽  
Definition Of ◽  
Better Than

ABSTRACT. The vicarious absolute calibration of electro-optical sensors dedicated to the Earth observation includes the definition of a reference surface from which radiometric measurements taken from the ground are compared to the effective radiance measured by the sensor in orbit. In order to facilitate the surface radiometric characterization process and consequently the sensor radiometric calibration, it is desirable that the surface presents, besides additional characteristics, temporal reflectance stability. This study aimed to evaluate the temporal stability of two potential reference surfaces for radiometric calibration of orbital electro-optical sensors located at: Tuz Gölü Salar in Turkey and Atacama Desert in Chile. Therefore, a temporal analysis of the radiometric properties of these two surfaces using cloud free images of TM/Landsat 5 sensor, acquired from 2003 to 2011, was performed. It was concluded, based on statistical criteria, that both reference surfaces do not presented temporal stability. Nevertheless, both surfaces may still be used for sensor calibration purposes if they were submitted to further spectral characterization with higher frequency and/or if the surfaces were considered stable “enough” within a certain limit of variation in reflectance. Taking that into account, according to the results of this work, it can be stated that Tuz G¨ol¨u surface reflectance has temporal stability within a range of 3-14% and the Atacama Desert better than 6%.Keywords: Earth observation sensors, radiometric calibration, reflectance, TM/Landsat 5.RESUMO. A primeira etapa para a realização da calibração absoluta de sensores de observação da Terra é a definição de uma superfície de referência. Um dos métodos mais comuns de calibração após o lançamento do sensor utiliza medições radiométricas de áreas localizadas na superfície terrestre. Para facilitar o processode caracterização da superfície e consequentemente o processo de calibração radiométrica, é desejável que a superfície apresente, entre outras características, estabilidade temporal. Assim, este trabalho teve como objetivo avaliar a estabilidade temporal de duas superfícies de referência potenciais para a calibração radiométrica de sistemas sensores eletro-ópticos: o salar de Tuz Gölü na Turquia e o deserto de Atacama no Chile. Para tanto, foi realizada uma análise temporal do comportamento espectral das duas superfícies por meio de imagens do sensor TMabordo do Landsat 5 livres de nuvens adquiridas nos anos de 2003 a 2011.De acordo com os resultados obtidos foi possível concluir, segundo os critérios estatísticos, que as duas superfícies de referência não apresentam estabilidade temporal. Apesar disso, as duas superfícies ainda podem ser utilizadas para calibração de sensores. Nesse caso, deve-se caracterizar espectralmente as duas áreas com maior frequência e/ou considerar a superfície como sendo “suficientemente” estável se a variação na reflectância ao longo do tempo for menor do que um determinado valor. Se esta consideração for feita pode-se afirmar, segundo o resultado desse trabalho, que Tuz Gölü tem estabilidade temporal entre 3 a 14% e o deserto de Atacama melhor do que 6%.Palavras-chave: sensores de observação da Terra, calibração radiométrica, reflectância, TM/Landsat 5.

scholarly journals SPECTRAL UNIFORMITY EVALUATION OF REFERENCE SURFACES FOR AIRBORNE AND ORBITAL SENSORS ABSOLUTE CALIBRATION

2012 ◽  
Vol 30 (3) ◽  
Author(s):  
Flávio Jorge Ponzoni ◽  
Cibele Teixeira Pinto ◽  
Ruy Morgado de Castro ◽  
Derek John Griffith
Keyword(s):  
Optical Sensors ◽  
Surface Characterization ◽  
Bare Soil ◽  
Quantitative Information ◽  
Earth Observation ◽  
Sensor Calibration ◽  
Absolute Calibration ◽  
Reference Surface ◽  
Earth Observation Satellites ◽  
Statistical Criteria

The extraction of quantitative information from data collected by either airborne or orbital electro optical sensors is only possible through a well-performed absolute calibration. The most common method of in-flight absolute calibration uses a reference surface. One of the most critical steps to implement this method is the reference surface characterization, which must be spectrally uniformity, among other features. This study presents the methodology used to assess the spectral uniformity of two potential areas for in-flight sensor calibration. Two surfaces were studied: (a) an area in Brazil of bare soil (quartz sand) and (b) TuzG ¨ol¨u salt flat in Turkey considered by the CEOS (Committee on Earth Observation Satellites) an official area for orbital sensors calibration. Radiometric measurements were carried out at various sampling points in these two areas. In addition, the study aims to describe and determine some of the main uncertainties sources involved in this process. According to the statistical criteria adopted, both reference surfaces have not been considered spectrally uniform.

scholarly journals New Approach for Temporal Stability Evaluation of Pseudo-Invariant Calibration Sites (PICS)

2019 ◽  
Vol 11 (12) ◽  
pp. 1502 ◽  
Author(s):  
Fatima Tuz Zafrin Tuli ◽  
Cibele Teixeira Pinto ◽  
Amit Angal ◽  
Xiaoxiong Xiong ◽  
Dennis Helder
Keyword(s):  
Temporal Stability ◽  
Kendall Test ◽  
Sensor Calibration ◽  
Landsat 8 ◽  
Radiometric Calibration ◽  
Calibration Source ◽  
Blue Band ◽  
New Approach ◽  
Monotonic Trend ◽  
Moderate Resolution Imaging Spectroradiometer

Pseudo-Invariant Calibration Sites (PICS) are one of the most popular methods for in-flight vicarious radiometric calibration of Earth remote sensing satellites. The fundamental question of PICS temporal stability has not been adequately addressed. However, the main purpose of this work is to evaluate the temporal stability of a few PICS using a new approach. The analysis was performed over six PICS (Libya 1, Libya 4, Niger 1, Niger 2, Egypt 1 and Sudan 1). The concept of a “Virtual Constellation” was developed to provide greater temporal coverage and also to overcome the dependence limitation of any specific characteristic derived from one particular sensor. TOA reflectance data from four sensors consistently demonstrating “stable” calibration to within 5%—the Landsat 7 ETM+ (Enhanced Thematic Mapper Plus), Landsat 8 OLI (Operational Land Imager), Terra MODIS (Moderate Resolution Imaging Spectroradiometer) and Sentinel-2A MSI (Multispectral Instrument)–were merged into a seamless dataset. Instead of using the traditional method of trend analysis (Student’s T test), a nonparametric Seasonal Mann-Kendall test was used for determining the PICS stability. The analysis results indicate that Libya 4 and Egypt 1 do not exhibit any monotonic trend in six reflective solar bands common to all of the studied sensors, indicating temporal stability. A decreasing monotonic trend was statistically detected in all bands, except SWIR 2, for Sudan 1 and the Green and Red bands for Niger 1. An increasing trend was detected in the Blue band for Niger 2 and the NIR band for Libya 1. These results do not suggest abandoning PICS as a viable calibration source. Rather, they indicate that PICS temporal stability cannot be assumed and should be regularly monitored as part of the sensor calibration process.

scholarly journals Derivation of Hyperspectral Profile of Extended Pseudo Invariant Calibration Sites (EPICS) for Use in Sensor Calibration

2019 ◽  
Vol 11 (19) ◽  
pp. 2279
Author(s):  
Mahesh Shrestha ◽  
Nahid Hasan ◽  
Larry Leigh ◽  
Dennis Helder
Keyword(s):  
North Africa ◽  
Temporal Stability ◽  
Critical Issue ◽  
Sensor Data ◽  
Sensor Calibration ◽  
Absolute Calibration ◽  
Time Interval ◽  
Calibration Model ◽  
Small Set ◽  
Cross Calibration

Reference of Earth-observing satellite sensor data to a common, consistent radiometric scale is an increasingly critical issue as more of these sensors are launched; such consistency can be achieved through radiometric cross-calibration of the sensors. A common cross-calibration approach uses a small set of regions of interest (ROIs) in established Pseudo-Invariant Calibration Sites (PICS) mainly located throughout North Africa. The number of available cloud-free coincident scene pairs available for these regions limits the usefulness of this approach; furthermore, the temporal stability of most regions throughout North Africa is not known, and limited hyperspectral information exists for these regions. As a result, it takes more time to construct an appropriate cross-calibration dataset. In a previous work, Shrestha et al. presented an analysis identifying 19 distinct “clusters” of spectrally similar surface cover that are widely distributed across North Africa, with the potential to provide near-daily cloud-free imaging for most sensors. This paper proposes a technique to generate a representative hyperspectral profile for these clusters. The technique was used to generate the profile for the cluster containing the largest number of aggregated pixels. The resulting profile was found to have temporal uncertainties within 5% across all the spectral regions. Overall, this technique shows great potential for generation of representative hyperspectral profiles for any North African cluster, which could allow the use of the entire North Africa Saharan region as an extended PICS (EPICS) dataset for sensor cross-calibration. This should result in the increased temporal resolution of cross-calibration datasets and should help to achieve a cross-calibration quality similar to that of individual PICS in a significantly shorter time interval. It also facilitates the development of an EPICS based absolute calibration model, which can improve the accuracy and consistency in simulating any sensor’s top of atmosphere (TOA) reflectance.

Spectral and Atmospheric Characterization of a Site at Atacama Desert for Earth Observation Sensor Calibration

2015 ◽  
Vol 12 (11) ◽  
pp. 2227-2231 ◽  
Author(s):  
Cibele T. Pinto ◽  
Flavio J. Ponzoni ◽  
C. Barrientos ◽  
C. Mattar ◽  
A. Santamaria-Artigas ◽  
...  
Keyword(s):  
Atacama Desert ◽  
Earth Observation ◽  
Sensor Calibration ◽  
A Site

scholarly journals KNOWLEDGE AND SKILLS RELATED TO ACTIVE OPTICAL SENSORS IN THE BODY OF KNOWLEDGE FOR EARTH OBSERVATION AND GEOINFORMATION (EO4GEO BOK)

2021 ◽  
Vol V-5-2021 ◽  
pp. 9-16
Author(s):  
C. Dubois ◽  
B. Jutzi ◽  
M. Olijslagers ◽  
C. Pathe ◽  
C. Schmullius ◽  
...  
Keyword(s):  
Optical Sensors ◽  
Earth Observation ◽  
The Body ◽  
Academic Training ◽  
Mobile Mapping ◽  
Knowledge And Skills ◽  
Training Requirements ◽  
Body Of Knowledge ◽  
Close Range ◽  
Definition Of

Abstract. The field of Earth Observation (EO) and Geoinformation (GI) is gaining more and more importance due to the increasing number of data and data processing algorithms to respond even more accurately to a variety of challenges in many application areas. In order to follow recent activities and align the exponential evolution of datasets and recent processing trends with market and academic training requirements, the EO*GI sector needs an updated and new definition of knowledge and skills. To this goal, a specific body of knowledge for Earth Observation and Geoinformation (EO4GEO BoK) is currently being implemented with the aim of providing interconnected concepts and job-oriented skills. One novelty of the BoK is to include topics related to Earth Observation, in particular to introduce the different sensors used in this field. Active optical sensors are at the crossroad between Earth Observation and close-range photogrammetry and have not been described in any other existing BoK. This paper introduces therefore the part of the EO4GEO BoK that is dedicated to active optical sensors. Such systems are used in various job-oriented applications such as archeology, mobile mapping, indoor or outdoor, or for surveying purposes, just to name a few. The structure of this part of the BoK is explained and specific descriptions and relationships between the identified concepts are given. Finally, the skills acquired by completing these BoK concepts are presented and discussed in terms of how they can be used in a professional context or in the definition of job-oriented learning paths.

scholarly journals Preliminary Selection and Characterization of Pseudo-Invariant Calibration Sites in Northwest China

2020 ◽  
Vol 12 (16) ◽  
pp. 2517
Author(s):  
Xiuqing Hu ◽  
Ling Wang ◽  
Junwei Wang ◽  
Lingli He ◽  
Lin Chen ◽  
...  
Keyword(s):  
Optical Sensors ◽  
Temporal Stability ◽  
Selection Procedure ◽  
Northwest China ◽  
Radiometric Calibration ◽  
Practical Utilization ◽  
Vicarious Calibration ◽  
Spatial Uniformity ◽  
Moderate Resolution Imaging Spectroradiometer ◽  
Spectral Imager

Pseudo-invariant calibration sites (PICS) have been used for the radiometric calibration and stability monitoring of satellite optical sensors. Several stable PICS, such as those in the Sahara Desert in North Africa, were selected for the vicarious calibration of earth remote sensing satellites. However, the selection procedure of PICSs in the whole of Northwest China has not been fully explored before. This paper presents a novel technique for selecting PICS in Northwest China by combined using the coefficient of variation (CV) and the iteratively reweighted multivariate alteration detection (IR-MAD) technique. IR-MAD, which calculates the differences between two multispectral N-band images from the same scene acquired at different times, is used to identify no-change pixels (NCPs) of the scene through one image pair. The NCPs from IR-MAD using the long-term data of FY-3 visible infrared radiometer (VIRR) and aqua Moderate Resolution Imaging Spectroradiometer (MODIS) were aggregated into the contiguously stable sites. The traditional spatial uniformity and temporal stability from MODIS surface products were used to select the potential PICS. By combining the results of both methods, over thirty PICSs with a wider brightness range of the scene types were selected. To confirm and characterize these PICSs over Northwest China, Landsat operational land imager (OLI) high-spatial-resolution images were used to check the spatial uniformity of the selected site to determine the specific location and the size of these sites. Additionally, the surface spectral reflectance and bidirectional reflectance distribution function (BRDF) were obtained from the field campaign at Chaidamu Basin, 2018. To demonstrate the practical utilization and usability of these PICSs, they were employed in the multi-site top of atmosphere (TOA) reflectance simulation to validate the operational calibration performance of Aqua/MODIS and FY-3D/MERSI-II (Medium Resolution Spectral Imager II). The simulation results showed good consistency compared with the observations from both MODIS and MERSI-II, with a relative bias and root mean square error (RMSE) of <5% and <0.05%, respectively. These sites provide prospects for multi-site vicarious calibrations of solar reflective bands, which may help to evaluate or characterize instrumental nonlinear responses using a wider signal dynamic from the sites in different seasons.

Resolution and measurement in the scanning electron microscope

1987 ◽  
Vol 45 ◽  
pp. 534-537 ◽  
Author(s):  
Michael T. Postek
Keyword(s):  
Electron Microscope ◽  
Scanning Electron Microscope ◽  
Engineering Design ◽  
Resolving Power ◽  
Practical Applications ◽  
Instrument Resolution ◽  
Accurate Definition ◽  
Definition Of ◽  
Scanning Electron ◽  
Better Than

The term ultimate resolution or resolving power is the very best performance that can be obtained from a scanning electron microscope (SEM) given the optimum instrumental conditions and sample. However, as it relates to SEM users, the conventional definitions of this figure are ambiguous. The numbers quoted for the resolution of an instrument are not only theoretically derived, but are also verified through the direct measurement of images on micrographs. However, the samples commonly used for this purpose are specifically optimized for the measurement of instrument resolution and are most often not typical of the sample used in practical applications.SEM RESOLUTION. Some instruments resolve better than others either due to engineering design or other reasons. There is no definitively accurate definition of how to quantify instrument resolution and its measurement in the SEM.

scholarly journals An orthogonal terrain-following coordinate and its preliminary tests using 2-D idealized advection experiments

2014 ◽  
Vol 7 (4) ◽  
pp. 1767-1778 ◽  
Author(s):  
Y. Li ◽  
B. Wang ◽  
D. Wang ◽  
J. Li ◽  
L. Dong
Keyword(s):  
Rotation Angle ◽  
Computational Grids ◽  
Time Step ◽  
Numerical Errors ◽  
Terrain Following ◽  
Steep Terrain ◽  
Definition Of ◽  
Σ Coordinate ◽  
Basis Vectors ◽  
Better Than

Abstract. We have designed an orthogonal curvilinear terrain-following coordinate (the orthogonal σ coordinate, or the OS coordinate) to reduce the advection errors in the classic σ coordinate. First, we rotate the basis vectors of the z coordinate in a specific way in order to obtain the orthogonal, terrain-following basis vectors of the OS coordinate, and then add a rotation parameter b to each rotation angle to create the smoother vertical levels of the OS coordinate with increasing height. Second, we solve the corresponding definition of each OS coordinate through its basis vectors; and then solve the 3-D coordinate surfaces of the OS coordinate numerically, therefore the computational grids created by the OS coordinate are not exactly orthogonal and its orthogonality is dependent on the accuracy of a numerical method. Third, through choosing a proper b, we can significantly smooth the vertical levels of the OS coordinate over a steep terrain, and, more importantly, we can create the orthogonal, terrain-following computational grids in the vertical through the orthogonal basis vectors of the OS coordinate, which can reduce the advection errors better than the corresponding hybrid σ coordinate. However, the convergence of the grid lines in the OS coordinate over orography restricts the time step and increases the numerical errors. We demonstrate the advantages and the drawbacks of the OS coordinate relative to the hybrid σ coordinate using two sets of 2-D linear advection experiments.

scholarly journals The Economic Value of Digital Earth

2019 ◽  
pp. 623-643 ◽  
Author(s):  
Max Craglia ◽  
Katarzyna Pogorzelska
Keyword(s):  
Common Good ◽  
Economic Value ◽  
Open Data ◽  
Earth Observation ◽  
Economic Approach ◽  
Scarce Resources ◽  
Digital Earth ◽  
Trade Offs ◽  
The Common ◽  
Definition Of

Abstract In this chapter, we approach the economic value of Digital Earth with a broad definition of economic value, i.e., the measure of benefits from goods or services to an economic agent and the trade-offs the agent makes in view of scarce resources. The concept of Digital Earth has several components: data, models, technology and infrastructure. We focus on Earth Observation (EO) data because this component has been undergoing the most dramatic change since the beginning of this century. We review the available recent studies to assess the value of EO/geospatial/open data and related infrastructures and identify three main sets of approaches focusing on the value of information, the economic approach to the value of EO to the economy from both macro- and microeconomic perspectives, and a third set that aims to maximize value through infrastructure and policy. We conclude that the economic value of Digital Earth critically depends on the perspective: the value for whom, what purpose, and when. This multiplicity is not a bad thing: it acknowledges that Digital Earth is a global concept in which everyone can recognize their viewpoint and collaborate with others to increase the common good.

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