Revisiting the sampling problem of satellite gravimetry – a perspective from the Bender configuration

2020 ◽  
Author(s):  
Anshul Yadav ◽  
Balaji Devaraju ◽  
Matthias Weigelt ◽  
Nico Sneeuw
Keyword(s):  
Spectral Resolution ◽  
General Pattern ◽  
Analytical Framework ◽  
Spectral Space ◽  
Signal Acquisition ◽  
Polar Gap ◽  
Sampling Problem ◽  
Global Coverage ◽  
Inclination Functions ◽  
East West

<p class="western" align="justify">The signal acquisition by the two different GRACE-like satellite pairs in a Bender configuration - polar and inclined, is dissimilar to each other. This difference is attributable to differing relative sampling geometry and global coverage. While the polar pair covers the entire globe, the inclined pair does not cover the higher latitudes leaving a local discontinuity around the poles in acquired signal (better known as the Polar Gap problem). Similarly, due to its north-south orientation, the polar pair can capture well the features that are predominantly oriented in the east-west direction. We simulated a Bender configuration using ESA's Earth System Model to see how the two satellite pairs contributed to the spherical harmonic coefficients. The general pattern was that the polar orbit contributed strongly to the zonal coefficients and the tesserals around it (near-zonal coefficients) while the inclined orbit contributed strongly to the other tesseral and the sectorial coefficients, which is well known. We also found out that the weak zonal and near-zonal inclined pair contributions lay inside a wedge in the spectral space, very similar to the polar gap error wedge. We want to discern how the satellites' relative geometry, particularly the polar gap issue in the inclined pair of a bender configuration, affects the solution's spectral resolution. In this study, we model the contribution coefficients of the polar and inclined pairs as a function of orbit geometries, employing the semi-analytical framework based on inclination functions. We hope that this will help <span lang="en-IN">in understanding the spectral resolution of the next generation gravity missions</span>.</p>

Sampling theorem of satellite gravimetry from the perspective of the Bender configuration

2021 ◽  
Author(s):  
Anshul Yadav ◽  
Balaji Devaraju ◽  
Matthias Weigelt ◽  
Nico Sneeuw
Keyword(s):  
Sampling Theorem ◽  
Precise Determination ◽  
Signal Acquisition ◽  
Satellite Gravimetry ◽  
Orbital Geometry ◽  
Spectral Coefficients ◽  
Satellite Geometry ◽  
Polar Gap ◽  
Regular Sampling ◽  
Inclination Functions

<p>Satellites in different orbital configurations acquire gravity signals differently. Thus, a difference in admissible spectral coefficients can be expected when the orbital geometry changes. A simple illustration of this phenomenon is seen in the Bender configuration of two GRACE-like satellite pairs - polar and inclined. In the Bender configuration, the polar pair covers the entire globe. In contrast, the inclined pair does not cover the higher latitudes leaving a local discontinuity around the poles in the acquired signal (better known as the <em>Polar Gap problem</em>). Similarly, due to its north-south orientation, the polar pair can capture the features that are predominantly oriented in the east-west direction. Trying to understand better the relationship between satellite geometry and signal acquisition led us to take our first steps in the direction of a unified sampling theory in satellite gravimetry. To this end, we employed the concepts behind the rotation of spherical harmonic coefficients built upon Inclination functions to express the geopotential functionals. Our work utilizes the Lomb-Scargle Periodogram based approach to ascertain limiting frequencies from the systemic quasi-regular sampling net formed on the satellite torus contrary to interpolation and FFT based techniques used in earlier such research endeavors. Through our work, we aim at improving our understanding of how the transformation of the geopotential occurs from the global to the spectral domain. We hope that this will help design future satellite missions with geometries best suited for their objective based on the precise determination of essential spectral coefficients.</p>

scholarly journals Aerosol direct radiative effect over clouds from synergy of OMI and MODIS reflectance

2019 ◽  
Author(s):  
Martin de Graaf ◽  
L. Gijsbert Tilstra ◽  
Piet Stammes
Keyword(s):  
Spatial Resolution ◽  
Spectral Resolution ◽  
Source Region ◽  
Data Retrieval ◽  
Radiative Effect ◽  
Aerosol Absorption ◽  
Ascension Island ◽  
Microphysical Parameters ◽  
Global Coverage ◽  
Shortwave Infrared

Abstract. The retrieval of geophysical parameters is increasingly dependent on synergistic use of satellite instruments. More sophisticated parameters can be retrieved and the accuracy of retrievals can be increased when more information is combined. In this paper, a synergistic application of OMI/Aura and MODIS/Aqua Level 1B reflectances is described, enabling the retrieval of the aerosol direct radiative effect (DRE) over clouds using the differential aerosol absorption (DAA) technique. This technique was first developed for reflectances from SCIAMACHY/Envisat, which had the unique capability of measuring contiguous radiances from the ultraviolet (UV) at 240 nm to 1750 nm in the shortwave-infrared (SWIR), at a moderate spectral resolution of 0.2–1.5 nm. However, the spatial resolution and global coverage of SCIAMACHY was limited, and Envisat stopped delivering data in 2012. In order to continue the DRE data retrieval, reflectances from OMI and MODIS, flying in formation, were combined from the UV to the SWIR. This resulted in reflectances at a limited but sufficient spectral resolution, available at the OMI pixel grid, which have a much higher spatial resolution and coverage than SCIAMACHY. The combined reflectance spectra allow the retrieval of cloud microphysical parameters in the SWIR, and the subsequent retrieval of aerosol DRE over cloud scenes using the DAA technique. The new aerosol DRE over clouds dataset from OMI/MODIS is compared to the SCIAMACHY dataset for the period 2006–2009, showing a very high correlation. The average aerosol DRE over clouds in August 2006 was 31.5 Wm−2 with a standard deviation of 16 Wm−2. The maximum daily averaged DRE from OMI/MODIS in August 2006 was 75.6 ± 13 Wm−2. Over the Atlantic Ocean, the OMI/MODIS DRE dataset is related to AOT measurements over Ascension Island in 2016, showing the transport of smoke all the way from its source region in Africa over the Atlantic to Ascension and beyond.

scholarly journals Global monitoring of terrestrial chlorophyll fluorescence from moderate-spectral-resolution near-infrared satellite measurements: methodology, simulations, and application to GOME-2

2013 ◽  
Vol 6 (10) ◽  
pp. 2803-2823 ◽  
Author(s):  
J. Joiner ◽  
L. Guanter ◽  
R. Lindstrot ◽  
M. Voigt ◽  
A. P. Vasilkov ◽  
...  
Keyword(s):  
Chlorophyll Fluorescence ◽  
Spectral Resolution ◽  
Hyperspectral Data ◽  
Radiative Transfer Model ◽  
High Signal ◽  
Transfer Model ◽  
Good Precision ◽  
Atmospheric Absorption ◽  
Red Fluorescence ◽  
Global Coverage

Abstract. Globally mapped terrestrial chlorophyll fluorescence retrievals are of high interest because they can provide information on the functional status of vegetation including light-use efficiency and global primary productivity that can be used for global carbon cycle modeling and agricultural applications. Previous satellite retrievals of fluorescence have relied solely upon the filling-in of solar Fraunhofer lines that are not significantly affected by atmospheric absorption. Although these measurements provide near-global coverage on a monthly basis, they suffer from relatively low precision and sparse spatial sampling. Here, we describe a new methodology to retrieve global far-red fluorescence information; we use hyperspectral data with a simplified radiative transfer model to disentangle the spectral signatures of three basic components: atmospheric absorption, surface reflectance, and fluorescence radiance. An empirically based principal component analysis approach is employed, primarily using cloudy data over ocean, to model and solve for the atmospheric absorption. Through detailed simulations, we demonstrate the feasibility of the approach and show that moderate-spectral-resolution measurements with a relatively high signal-to-noise ratio can be used to retrieve far-red fluorescence information with good precision and accuracy. The method is then applied to data from the Global Ozone Monitoring Instrument 2 (GOME-2). The GOME-2 fluorescence retrievals display similar spatial structure as compared with those from a simpler technique applied to the Greenhouse gases Observing SATellite (GOSAT). GOME-2 enables global mapping of far-red fluorescence with higher precision over smaller spatial and temporal scales than is possible with GOSAT. Near-global coverage is provided within a few days. We are able to show clearly for the first time physically plausible variations in fluorescence over the course of a single month at a spatial resolution of 0.5° × 0.5°. We also show some significant differences between fluorescence and coincident normalized difference vegetation indices (NDVI) retrievals.

scholarly journals Politik und ihre Grenzen in Clausewitz' Denken über den Krieg

2020 ◽  
Author(s):  
Tobias Wille
Keyword(s):  
Political Violence ◽  
18Th Century ◽  
Analytical Framework ◽  
Theoretical System ◽  
New Wars ◽  
Raison D’État ◽  
Theory Of War ◽  
East West

[Article in German; English title: "Politics and its limits in Clausewitz's thought on war"] Carl von Clausewitz's thought on war represents in a paradigmatic fashion an instrumental conception of violence in politics. For Clausewitz, violence is a means used in war to achieve political ends. Since the end of the East-West conflict, however, it is widely thought that Clausewitz's ideas are no longer applicable. Current forms of war may be violent, it is said, but they are no longer political because they are not waged by states alone, for the raison d'état narrowly conceived. This objection, however, rests on a misunderstanding of Clausewitz's concept of politics. This article seeks to reconstruct this concept systematically. It offers an interpretation whereby "politics" in Clausewitz's theoretical system denotes an interaction of two or more actors, each of whom wants to realize their respective will but whose wills cannot be fully reconciled. For Clausewitz, war is such politics that is conducted by violent means. Against this background, it is argued that Clausewitz's theory of war provides a fruitful analytical framework to understand the transformations of political violence from the cabinet wars of the 18th century to the "new wars" of our time.

scholarly journals The power of the dead in Neolithic landscapes: an agricultural-celestial metaphor in the funerary tradition of the Funnel Beaker Culture in the Sandomierz Upland

2016 ◽  
Vol 43 ◽  
pp. 429-444
Author(s):  
Stanislaw Iwaniszewski
Keyword(s):  
General Pattern ◽  
Landscape Archaeology ◽  
The Dead ◽  
Funnel Beaker Culture ◽  
East West

FBC earthen long barrows were roughly oriented along the East-West axis, with deviations not exceeding the frame of the solar arc. Also, the Sandomierz Group monuments display this general pattern. The paper brings together archaeoastronomy, landscape archaeology and symbolic archaeology.

scholarly journals DATA PROCESSING FOR THE SPACE-BASED DESIS HYPERSPECTRAL SENSOR

2017 ◽  
Vol XLII-1/W1 ◽  
pp. 271-277 ◽  
Author(s):  
E. Carmona ◽  
J. Avbelj ◽  
K. Alonso ◽  
M. Bachmann ◽  
D. Cerra ◽  
...  
Keyword(s):  
Data Processing ◽  
Spectral Resolution ◽  
Space Station ◽  
Hyperspectral Data ◽  
High Spectral Resolution ◽  
Imaging Spectrometer ◽  
Cmos Sensor ◽  
Global Coverage ◽  
German Aerospace ◽  
Hyperspectral Sensor

The German Aerospace Center (DLR) and Teledyne Brown Engineering (TBE) have established a collaboration to develop and operate a new space-based hyperspectral sensor, the DLR Earth Sensing Imaging Spectrometer (DESIS). DESIS will provide spacebased hyperspectral data in the VNIR with high spectral resolution and near-global coverage. While TBE provides the platform and infrastructure for operation of the DESIS instrument on the International Space Station, DLR is responsible for providing the instrument and the processing software. The DESIS instrument is equipped with novel characteristics for an imaging spectrometer such high spectral resolution (2.55 nm), a mirror pointing unit or a CMOS sensor operated in rolling shutter mode. We present here an overview of the DESIS instrument and its processing chain, emphasizing the effect of the novel characteristics of DESIS in the data processing and final data products. Furthermore, we analyse in more detail the effect of the rolling shutter on the DESIS data and possible mitigation/correction strategies.

Axial Observation of X-Ray Spectra from a Beam-Foil Source

1988 ◽  
Vol 102 ◽  
pp. 339-342
Author(s):  
J.M. Laming ◽  
J.D. Silver ◽  
R. Barnsley ◽  
J. Dunn ◽  
K.D. Evans ◽  
...  
Keyword(s):  
Spectral Resolution ◽  
Heavy Ion ◽  
Ion Beams ◽  
Beam Axis ◽  
Doppler Broadening ◽  
X Ray ◽  
Beam Foil

AbstractNew observations of x-ray spectra from foil-excited heavy ion beams are reported. By observing the target in a direction along the beam axis, an improvement in spectral resolution, δλ/λ, by about a factor of two is achieved, due to the reduced Doppler broadening in this geometry.

Values and intergroup perceptions of East Germans and West Germans in 1998 1This research was supported by a grant from the German Research Society (We 1106/3-1).

1999 ◽  
Vol 58 (4) ◽  
pp. 263-272
Author(s):  
Jörg Doll ◽  
Michael Dick
Keyword(s):  
Research Society ◽  
Frame Of Reference ◽  
Control Group ◽  
Perceived Similarity ◽  
The West ◽  
Need For Uniqueness ◽  
German Research ◽  
East German ◽  
Experimental Group ◽  
East West

The studies reported here focus on similarities and dissimilarities between the terminal value hierarchies ( Rokeach, 1973 ) ascribed to different groups ( Schwartz & Struch, 1990 ). In Study 1, n = 65 East Germans and n = 110 West Germans mutually assess the respective ingroup and outgroup. In this intra-German comparison the West Germans, with a mean intraindividual correlation of rho = 0.609, perceive a significantly greater East-West similarity between the group-related value hierarchies than the East Germans, with a mean rho = 0.400. Study 2 gives East German subjects either a Swiss (n = 58) or Polish (n = 59) frame of reference in the comparison between the categories German and East German. Whereas the Swiss frame of reference should arouse a need for uniqueness, the Polish frame of reference should arouse a need for similarity. In accordance with expectations, the Swiss frame of reference significantly reduces the correlative similarity between German and East German from a mean rho = 0.703 in a control group (n = 59) to a mean rho = 0.518 in the experimental group. Contrary to expectations, the Polish frame of reference does not lead to an increase in perceived similarity (mean rho = 0.712).

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