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On the retrieval of ice sheet temperature profile by means of low frequency wide band radiometry: sensitivity to the physical parameters
No full textIn a climate change era, improved information on ice sheets and ices shelves are required in order to monitor theirs changes
and the possible contribution to sea level rise over the 21st century and beyond ([1], WCRP). In recent years activities were
promoted by SCAR, CliC (WCRP), IASC, to improve models for predicting the future evolution of ice sheets and significant
progress has been reported [2]. Nevertheless, there are still large discrepancies between simulations [3, 4, 5] and large uncer-
tainties still remain related to our limited quantitative understanding of many of the processes that control the mass balance and
stability of ice sheets, and the inability to characterize such processes from space using existing or planned sensors. Foremost
among them is the vertical temperature profile within the ice, which is sparsely measured in situ, but is a primary control on the
rate at which ice flows by deformation. With the launch of L-band radiometers (SMOS, Aquarius, SMAP), which are capable
of observing ice sheet in depth, a new methodology was proposed to infer information by using satellite data and glaciological
models [6]. More recently, the use of microwave radiometry in a low frequencies range (i.e., a wide range 0.50–2.00 GHz)
was suggested to go deeper in the ice and retrieve the ice sheet and shelf temperature profile (i.e., from the top to the bottom)
through the use of techniques similar to those used by radiometric atmospheric sounders [7] and proposals for space mission
development are in preparation in Europe and U.S. The methodology was already successfully tested in airborne campaigns
in both Greenland and Antarctica [8, 9]. With the purpose of developing an operational ice sheet/shelf temperature retrieval
methodology appliable to spaceborne data, a model analysis started to better understand the contribution of observed brightness
temperature at the different frequencies as a function of depth.
The analysis was conducted by using a microwave emission model [10], able to simulate the brightness temperature, which
use as inputs the ice temperature and density profiles based on glaciological models [11, 12]. Ice sheet is discretized by 2-m
thick layers between surface and 50m in depth, then 50-m layers down to the bedrock. This allows to a better characterization
of the upper part of the ice sheet where the most rapid ice density changes happened. As the horizontal advection is neglected
in this model, the validity area is limited where the ice velocity [13] is lower than 10m yr-1. Four geophysical parameters
(i.e., ice thickness, surface temperature, snow accumulation, and geothermal heat flux) are needed to run models. Analysis
was performed over all Antarctica and information on these parameters are derived from literature [14, 15, 16, 17]. For each
considered 25×25km pixel, the nominal values for ice thickness (H), surface temperature (Tsurf), snow accumulation (Acc),
and geothermal heat flux (GHF) were used to compute the TB. Moreover, for the three last parameters, theirs uncertainty was
considered as follows: Tsurf±1.5K, and Acc±0.5 Acc. Regarding GHF, its value was transformed in a basal temperature (Tbasal)
by means of Robin model and the uncertainties were considered as Tbasal±4.5K.
In addition to TB, and to provide detailed information about the contribution of each ice sheet layer to the observed TB, the
weighting function has been computed [18, 19]. Considering that:
̃T ice
B =
∫ H
0
T (z) W (z) dz (1)
where T(z) is the temperature of the ice layer, the weighting function (W(z)) can be defined
W is the weight of the considered layer, ke is the extinction coefficient, and z is the depth.
Based on the weight computation, it is possible to identify for each frequency the ice sheet part proving the maximum
contribution to the signal. For that, the minimum thick of the normalized weight representing the 90% of the total weight
has been calculated. The portion of the function that subtend this percentage has been identified using a rolling integral. The
upper (ztop) and lower (zbottom) limits of these intervals have been calculated together with their differences (∆z). These values
were then normalized to the thickness in order to compare values within the continent and, finally, the uncertainty (σ∆z) was
calculated by considering the range of variability for all the parameters. Sensitivity to single parameters was also computed and
it was demonstrated that TB is function of H and Tsurf, but also Acc and GHF could influence TB under specific site conditions.
Obtained Results are summarized in Fig. 1 where ztop, zbottom, ∆z, and σ∆z maps of Antarctica are represented at 0.50,
0.95, 1.40, and 1.85 GHz respectively. At 0.50 GHz the lower 50% of the ice column contribute to the 90% of the simulated
TB with the zbottom always located at the ice/bedrock interface. Consequently, the first half of the ice column, including the
surface, shows a limited contribute to the total emission. The uncertainty to different parameters is then limited. Increasing the
frequency, ztop and zbottom rise in the ice column up to the surface, ∆z decreases and uncertainty increases at 0.95 and 1.40 GHz.
At 1.85 GHz uncertainty is low because it is less sensitive to GHF and accumulation variability.
These results confirmed that different frequencies are sensitive to different portion of the ice column and then can be used
to better estimate different geophysical parameters and constrain the ice temperature profile. Moreover, lowest and highest
frequencies could be used to constrain geothermal heat flux and surface temperature, respectively, with a relatively small
uncertainty whereas frequencies in the 0.95–1.40 GHz range could be potentially used to constrain snow accumulation even if
with a higher error. In addition, simulations show that in the inner part of Antarctica ice sheet TB decreases with frequency
while close to the coast the TB is almost frequency independent. Also, this information could be used to constraints the retrieval
depending on location. Detailed analysis of the obtained results and the advanced retrieval method will be presented at the
conference
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
CRYORAD: a new mission concept for monitoring the crysophere based on low frequency wideband radiometry
No full textVariations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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