scholarly journals Greenland Ice Mapping Project: ice flow velocity variation at sub-monthly to decadal timescales

2018 ◽  
Vol 12 (7) ◽  
pp. 2211-2227 ◽  
Author(s):  
Ian Joughin ◽  
Ben E. Smith ◽  
Ian Howat
Keyword(s):  
Flow Speed ◽  
Velocity Variation ◽  
Landsat 8 ◽  
North West ◽  
South West ◽  
Speed Up ◽  
Ice Velocity ◽  
Year 2000 ◽  
The Impact ◽  
Good Agreement

Abstract. We describe several new ice velocity maps produced by the Greenland Ice Mapping Project (GIMP) using Landsat 8 and Copernicus Sentinel 1A/B data. We then focus on several sites where we analyse these data in conjunction with earlier data from this project, which extend back to the year 2000. At Jakobshavn Isbræ and Køge Bugt, we find good agreement when comparing results from different sensors. In a change from recent behaviour, Jakobshavn Isbræ began slowing substantially in 2017, with a midsummer peak that was even slower than some previous winter minima. Over the last decade, we identify two major slowdown events at Køge Bugt that coincide with short-term advances of the terminus. We also examined populations of glaciers in north-west and south-west Greenland to produce a record of speed-up since 2000. Collectively these glaciers continue to speed up, but there are regional differences in the timing of periods of peak speed-up. In addition, we computed trends in winter flow speed for much of the south-west margin of the ice sheet and find little in the way of statistically significant changes over the period covered by our data. Finally, although the consistency of the data is generally good over time and across sensors, our analysis indicates that substantial differences can arise in regions with high strain rates (e.g. shear margins) where sensor resolution can become a factor. For applications such as constraining model inversions, users should factor in the impact that the data's resolution has on their results.

scholarly journals Greenland Ice Mapping Project: Ice Flow Velocity Variation at submonthly to decadal time scales

2018 ◽  
Author(s):  
Ian Joughin ◽  
Ben E. Smith ◽  
Ian Howat
Keyword(s):  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Velocity Variation ◽  
Landsat 8 ◽  
Ice Flow ◽  
Speed Up ◽  
Ice Velocity ◽  
Year 2000 ◽  
The Impact ◽  
Ice Sheet Mapping

Abstract. We describe several new ice velocity maps produced by the Greenland Ice Sheet Mapping Project (GIMP) using Landsat 8 and Copernicus Sentinel 1A/B data. We then focus on several sites where we analyse these data in conjunction with earlier data from this project, which extend back to the year 2000. At Jakobshavn Isbrae and Koge Bugt, we find good agreement when comparing results from different sensors. In a change from recent behaviour, Jakobshavn Isbrae began slowing substantially in 2017, with a mid-summer peak that was even slower than some previous winter minimums. Over the last decade, we identify two major slowdown events at Koge Bugt that coincide with short-term advances of the terminus. We also examined populations of glaciers in northwest and southwest Greenland to produce a record of speedup since 2000. Collectively these glaciers continue to speed up, but there are regional differences in the timing of periods of peak speedup. In addition, we computed trends for much of the southwest margin of the ice sheet where other work has suggested slowing ice flow in response to increased melting. Contrary to the earlier results, we find no evidence for a slowdown distributed over a wide area. Finally, although consistency of the data generally is good through time and across sensors, our analysis indicates substantial differences can arise in regions with high strain rates (e.g., shear margins) where sensor resolution can become a factor. For applications such as constraining model inversions, users should factor in the impact that the data's resolution has on their results.

scholarly journals The Impact of Armed Conflict on Agro-Industrial Development in Cameroon: The case of the Cameroon Development Corporation (CDC) within the context of the Anglophone crisis

2020 ◽  
Vol 8 (12) ◽  
pp. 279-288
Author(s):  
Dinsi Stanley Chung ◽  
Keyword(s):  
Armed Conflict ◽  
Industrial Development ◽  
Financial Loss ◽  
North West ◽  
The North ◽  
South West ◽  
Study Results ◽  
Development Corporation ◽  
English Speaking ◽  
The Impact

The Cameroon Development Corporation has been severely affected by the armed conflict in the English speaking (North West and South West regions) part of the country that has been on for close to four years running. How then has the armed conflict in the North West and South West regions of Cameroon affected the Cameroon Development Corporation? How can the growth of the agro-industry be guaranteed? This study looks at the impact of the armed conflict in the North West and South West regions of Cameroon on the Cameroon Development Corporation. Making use of public policy theories, this study establishes a link between government defense strategies/sector development policies and agro-industrial development. The study results show that due to the armed conflict in the English speaking regions, the CDC has incurred major damages including: loss in human capital, drop in production capacity, heavy financial loss and equipment damages. The study results also reveal that, the survival of the CDC depends largely on strategic options to be taken at two separate levels including: political options by conflicting parties - the government and separatist fighters on the one hand, and on the other, options taken by the CDC at both managerial and technical levels. The study concludes that for the CDC to attain structural growth and development that will significantly contribute to the national economy, conflicting.

scholarly journals A complete map of Greenland ice velocity derived from satellite data collected over 20 years

2017 ◽  
Vol 64 (243) ◽  
pp. 1-11 ◽  
Author(s):  
IAN JOUGHIN ◽  
BEN E. SMITH ◽  
IAN M. HOWAT
Keyword(s):  
Flow Velocity ◽  
Feature Tracking ◽  
Ice Sheet ◽  
Synthetic Aperture ◽  
Landsat 8 ◽  
Ice Flow ◽  
Interferometric Phase ◽  
Ice Velocity ◽  
Slow Moving ◽  
Good Agreement

ABSTRACTWhile numerous maps of Greenland ice flow velocity exist, most have gaps in coverage and/or accuracy is limited. We processed a large volume of synthetic aperture radar and Landsat 8 imagery collected between 1995 and 2015 to produce a nearly complete map of ice flow velocity for Greenland at a far greater accuracy than most prior products. We evaluated the accuracy of this map by comparing it with a variety of measured and estimated velocities. For the slow-moving interior of the ice sheet, where estimates are determined from interferometric phase, the errors are ~2 m a−1 or better. For coastal areas, where estimates are determined entirely from speckle- or feature-tracking methods, errors are 2–3 m a−1, which is in good agreement with the estimated formal errors. Especially for the slow-moving majority of the ice sheet, this map provides an important source of data for numerous types of glaciological studies.

scholarly journals Retrieval of tropospheric NO<sub>2</sub> columns over Berlin from high-resolution airborne observations with the spectrolite breadboard instrument

2017 ◽  
Author(s):  
Tim Vlemmix ◽  
Xinrui (Jerry) Ge ◽  
Bryan T. G. de Goeij ◽  
Len F. van der Wal ◽  
Gerard C. J. Otter ◽  
...  
Keyword(s):  
Prior Information ◽  
Urban Region ◽  
Landsat 8 ◽  
Surface Reflectance ◽  
Spectral Measurements ◽  
Retrieval Method ◽  
Tropospheric No2 ◽  
The Impact ◽  
Thickness Measurements ◽  
Good Agreement

Abstract. This paper presents the retrieval method that was developed to derive tropospheric NO2 columns from UV/VIS spectral measurements obtained with the Spectrolite Breadboard Instrument during the AROMAPEX campaign in Berlin (April 2016). A typical DOAS retrieval approach is followed. For the calculation of air mass factors this study specifically focuses on the impact of the surface reflectance, which varies considerably from pixel to pixel over this urban region. Ground-based aerosol optical thickness measurements are used as prior information. It is shown that retrieved surface reflectance shows good agreement with those derived from Landsat 8 measurements performed on the same day. Furthermore we demonstrate that tropospheric NO2 columns retrieved for pairs of adjacent pixels are self-consistent in the sense that they do not show a substantial systematic dependence on surface reflectance, in contrast to differential slant column densities. Also some cases are identified to illustrate this on a pixel-by-pixel level. An error budget is provided to quantify the impact of various assumptions on the accuracy of the retrieval of surface reflectance and tropospheric NO2 columns. Both in the morning and afternoon flight a NO2 plume is observed stretching out over Berlin from West to East. Peak values between 15 × 1015 and 20 × 1015 molec/cm2 are detected, whereas – at much lower spatial resolution – OMI detects peak values between 9 × 1015 (first overpass) and 4 × 1015 molec/cm2 (second overpass).

scholarly journals The effect of the ongoing civil strife on key immunisation outcomes in the North West and South West regions of Cameroon

2021 ◽  
Vol 15 (1) ◽  
Author(s):  
Yauba Saidu ◽  
Marius Vouking ◽  
Andreas Ateke Njoh ◽  
Hassan Ben Bachire ◽  
Calvin Tonga ◽  
...  
Keyword(s):  
Negative Impact ◽  
Healthcare Delivery ◽  
Management Tool ◽  
Conflict Zones ◽  
Civil Strife ◽  
North West ◽  
Vaccine Preventable Diseases ◽  
The North ◽  
South West ◽  
The Impact

Abstract Background Civil strife has long been recognized as a significant barrier in the fight against vaccine preventable diseases in several parts of the world. However, little is known about the impact of the ongoing civil strife on the immunisation system in the Northwest (NW) and Southwest (SW) regions of Cameroon, which erupted in late 2016. In this paper, we assessed the effect of the conflict on key immunisation outcomes in the North West and South West regions of Cameroon. Methods Data were obtained from the standard EPI data reporting tool, the District Vaccine and Data Management Tool (DVDMT), from all the districts in the two regions. Completed forms were then reviewed for accuracy prior to data entry at central level. Summary statistics were used to estimate the variables of interest for each region for the years 2016 (pre-conflict) and 2019 (during conflict). Results In the two regions, the security situation has deteriorated in almost all districts, which in turn has disrupted basic healthcare delivery in those areas. A total of 26 facilities were destroyed and 11 healthcare workers killed in both regions. Reported immunisation coverage rates for key antigens including, BCG, DPT-3 and MR, witnessed a dramatic decline between 2016 and 2019, ranging from 22% points decline for BCG in the NW and to 42% points decline for DPT-3 in the SW. Similarly, the proportion of districts with DPT-3 coverage of at least 80% dropped from 75% in 2016 to 11% in 2019 in the NW. In the SW this proportion dropped from 16% in 2016 to 0 % in 2019. Conclusion Our data demonstrates the marked negative impact of the ongoing civil strife on key immunisation outcomes in the two regions and the country at large. This decline could amplify the risk of vaccine preventable diseases vaccine preventable diseases outbreaks in the two regions. Besides the ongoing actions to contain the crises, effective strategies for reaching children in the conflict zones as well as the internally displaced population are needed. There is also the need to rebuild destroyed facilities as well as to protect health facilities and staff from targeted violence.

Were Textiles used as Money in Khotan in the Seventh and Eighth Centuries?

2013 ◽  
Vol 23 (2) ◽  
pp. 307-325 ◽  
Author(s):  
QING DUAN ◽  
HELEN WANG
Keyword(s):  
Everyday Life ◽  
Ethnic Groups ◽  
Sixth Century ◽  
Traditional Practices ◽  
Documentary Evidence ◽  
Unique Combination ◽  
North West ◽  
The North ◽  
South West ◽  
The Impact

The kingdom of Khotan lay 2,628 kilometres to the north-west of the Tang capital at Chang'an. Strategically located in the south-west of the Taklamakan Desert, Khotan was a meeting point of different ethnic groups, languages, cultures and traditions, and was renowned as a centre of Buddhism. With its unique combination of influences, Khotanese society was quite different from that of Turfan to the north of the Taklamakan. In addition to the indigenous practices and traditions that developed in Khotan, this kingdom was always under the influence of major external political powers: Khotan was a vassal kingdom of the Hephtalites or Turkic peoples during the sixth century, came under increasing Chinese influence in the seventh and eighth centuries, was under Tibetan occupation from the 790s to 840s, and thereafter under the Chinese again. The secular documentary evidence from Khotan, written in Khotanese and Chinese, from the seventh and eighth centuries reflects everyday life there, and reveals the impact of Chinese administrative changes on traditional practices.

Modeling of Tread Block Contact Mechanics Using Linear Viscoelastic Theory3

2008 ◽  
Vol 36 (3) ◽  
pp. 211-226 ◽  
Author(s):  
F. Liu ◽  
M. P. F. Sutcliffe ◽  
W. R. Graham
Keyword(s):  
High Speed ◽  
Slip Rate ◽  
Material Model ◽  
Contact Forces ◽  
Block Modeling ◽  
Rate Dependent ◽  
Linear Viscoelastic Material ◽  
Linear Viscoelastic ◽  
The Impact ◽  
Good Agreement

Abstract In an effort to understand the dynamic hub forces on road vehicles, an advanced free-rolling tire-model is being developed in which the tread blocks and tire belt are modeled separately. This paper presents the interim results for the tread block modeling. The finite element code ABAQUS/Explicit is used to predict the contact forces on the tread blocks based on a linear viscoelastic material model. Special attention is paid to investigating the forces on the tread blocks during the impact and release motions. A pressure and slip-rate-dependent frictional law is applied in the analysis. A simplified numerical model is also proposed where the tread blocks are discretized into linear viscoelastic spring elements. The results from both models are validated via experiments in a high-speed rolling test rig and found to be in good agreement.

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