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"Cunningham, G."
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Volcanologist
Introduces the field of volcanology, explaining the necessary educational steps, useful character traits, potential hazards, and daily job tasks related to this occupation.
Book
Variability of Arctic sea ice thickness and volume from CryoSat-2
We present our estimates of the thickness and volume of the Arctic Ocean ice cover from CryoSat-2 data acquired between October 2010 and May 2014. Average ice thickness and draft differences are within 0.16 m of measurements from other sources (moorings, submarine, electromagnetic sensors, IceBridge). The choice of parameters that affect the conversion of ice freeboard to thickness is discussed. Estimates between 2011 and 2013 suggest moderate decreases in volume followed by a notable increase of more than 2500 km3 (or 0.34 m of thickness over the basin) in 2014, which could be attributed to not only a cooler summer in 2013 but also to large-scale ice convergence just west of the Canadian Arctic Archipelago due to wind-driven onshore drift. Variability of volume and thickness in the multiyear ice zone underscores the importance of dynamics in maintaining the thickness of the Arctic ice cover. Volume estimates are compared with those from ICESat as well as the trends in ice thickness derived from submarine ice draft between 1980 and 2004. The combined ICESat and CryoSat-2 record yields reduced trends in volume loss compared with the 5 year ICESat record, which was weighted by the record-setting ice extent after the summer of 2007.
Journal Article
Multipolicy decision-making for autonomous driving via changepoint-based behavior prediction: Theory and experiment
This paper reports on an integrated inference and decision-making approach for autonomous driving that models vehicle behavior for both our vehicle and nearby vehicles as a discrete set of closed-loop policies. Each policy captures a distinct high-level behavior and intention, such as driving along a lane or turning at an intersection. We first employ Bayesian changepoint detection on the observed history of nearby cars to estimate the distribution over potential policies that each nearby car might be executing. We then sample policy assignments from these distributions to obtain high-likelihood actions for each participating vehicle, and perform closed-loop forward simulation to predict the outcome for each sampled policy assignment. After evaluating these predicted outcomes, we execute the policy with the maximum expected reward value. We validate behavioral prediction and decision-making using simulated and real-world experiments.
Journal Article
القيادة التربوية : مدخل قائم على حل المشكلات
يقدم هذا الكتاب مناقشة شاملة لمجال الادارة التربوية ويصف كيف تعمل المدارس الفعالة والناجحة والمديرون في بيئة متزايدة التحدي وسريعة التطور وملحة، بل قد تتسم بطابع ثوري، ويضع هذا الكتاب اما القراء مشهدا متكاملا للأساس المعرفي والبحثي فضلا عن ممارسة الإدارة من خلال سياق متعددة الزوايا ومساحة عريضة في التفكير.
Book
Thinning and volume loss of the Arctic Ocean sea ice cover: 2003-2008
We present our best estimate of the thickness and volume of the Arctic Ocean ice cover from 10 Ice, Cloud, and land Elevation Satellite (ICESat) campaigns that span a 5‐year period between 2003 and 2008. Derived ice drafts are consistently within 0.5 m of those from a submarine cruise in mid‐November of 2005 and 4 years of ice draft profiles from moorings in the Chukchi and Beaufort seas. Along with a more than 42% decrease in multiyear (MY) ice coverage since 2005, there was a remarkable thinning of ∼0.6 m in MY ice thickness over 4 years. In contrast, the average thickness of the seasonal ice in midwinter (∼2 m), which covered more than two‐thirds of the Arctic Ocean in 2007, exhibited a negligible trend. Average winter sea ice volume over the period, weighted by a loss of ∼3000 km3 between 2007 and 2008, was ∼14,000 km3. The total MY ice volume in the winter has experienced a net loss of 6300 km3 (>40%) in the 4 years since 2005, while the first‐year ice cover gained volume owing to increased overall area coverage. The overall decline in volume and thickness are explained almost entirely by changes in the MY ice cover. Combined with a large decline in MY ice coverage over this short record, there is a reversal in the volumetric and areal contributions of the two ice types to the total volume and area of the Arctic Ocean ice cover. Seasonal ice, having surpassed that of MY ice in winter area coverage and volume, became the dominant ice type. It seems that the near‐zero replenishment of the MY ice cover after the summers of 2005 and 2007, an imbalance in the cycle of replenishment and ice export, has played a significant role in the loss of Arctic sea ice volume over the ICESat record.
Journal Article
Contribution of melt in the Beaufort Sea to the decline in Arctic multiyear sea ice coverage: 1993-2009
For the summers of 1993 through 2009, we estimate the loss of multiyear sea ice (MYI) area in the Beaufort Sea due to melt. Parcels of MYI in April are traced into the Beaufort Sea where they melt as the ice edge retreats. Net loss of area (with fractional MYI coverage >50%) over the 17‐year period is ∼900 × 103 km2. Three‐quarters of that area, ∼10% of the area of the Arctic Ocean, was lost after 2000. There is a clear positive trend in the record, with a distinct peak of 213 × 103 km2 in 2008; this is twice the summer outflow at the Fram Strait that year. The net melt area of 490 × 103 km2 between 2005 and 2008 accounts for nearly 32% of the net loss of 1.54 × 106 km2 of Arctic Ocean MYI coverage over the same period. Volume loss, for the years with ICESat thickness (2004–2009), is highest at 473 km3 in 2008 followed by 320 km3 in 2007. Net loss in MYI volume for the six summers is ∼1400 km3. This is ∼20% of the loss in MYI volume of 6300 km3 during 2004–2008. This adds to the freshwater content of the Arctic Ocean and locally to the freshening of the Beaufort Gyre.
Journal Article
The OSIRIS-REx Laser Altimeter (OLA) Investigation and Instrument
The Canadian Space Agency (CSA) has contributed to the Origins Spectral Interpretation Resource Identification Security-Regolith Explorer (OSIRIS-REx) spacecraft the OSIRIS-REx Laser Altimeter (OLA). The OSIRIS-REx mission will sample asteroid 101955 Bennu, the first B-type asteroid to be visited by a spacecraft. Bennu is thought to be primitive, carbonaceous, and spectrally most closely related to CI and/or CM meteorites. As a scanning laser altimeter, the OLA instrument will measure the range between the OSIRIS-REx spacecraft and the surface of Bennu to produce digital terrain maps of unprecedented spatial scales for a planetary mission. The digital terrain maps produced will measure
∼
7
cm
per pixel globally, and
∼
3
cm
per pixel at specific sample sites. In addition, OLA data will be used to constrain and refine the spacecraft trajectories. Global maps and highly accurate spacecraft trajectory estimates are critical to infer the internal structure of the asteroid. The global and regional maps also are key to gain new insights into the surface processes acting across Bennu, which inform the selection of the OSIRIS-REx sample site. These, in turn, are essential for understanding the provenance of the regolith sample collected by the OSIRIS-REx spacecraft. The OLA data also are important for quantifying any hazards near the selected OSIRIS-REx sample site and for evaluating the range of tilts at the sampling site for comparison against the capabilities of the sample acquisition device.
Journal Article
Normal hearing is not enough to guarantee robust encoding of suprathreshold features important in everyday communication
\"Normal hearing\" is typically defined by threshold audibility, even though everyday communication relies on extracting key features of easily audible sound, not on sound detection. Anecdotally, many normal-hearing listeners report difficulty communicating in settings where there are competing sound sources, but the reasons for such difficulties are debated: Do these difficulties originate from deficits in cognitive processing, or differences in peripheral, sensory encoding? Here we show that listeners with clinically normal thresholds exhibit very large individual differences on a task requiring them to focus spatial selective auditory attention to understand one speech stream when there are similar, competing speech streams coming from other directions. These individual differences in selective auditory attention ability are unrelated to age, reading span (a measure of cognitive function), and minor differences in absolute hearing threshold; however, selective attention ability correlates with the ability to detect simple frequency modulation in a clearly audible tone. Importantly, we also find that selective attention performance correlates with physiological measures of how well the periodic, temporal structure of sounds above the threshold of audibility are encoded in early, subcortical portions of the auditory pathway. These results suggest that the fidelity of early sensory encoding of the temporal structure in suprathreshold sounds influences the ability to communicate in challenging settings. Tests like these may help tease apart how peripheral and central deficits contribute to communication impairments, ultimately leading to new approaches to combat the social isolation that often ensues.
Journal Article