Modelling the diurnal variations of urban heat islands with multi-source satellite data

Examination of the diurnal variations in surface urban heat islands (UHIs) has been hindered by incompatible spatial and temporal resolutions of satellite data. In this study, a diurnal temperature cycle genetic algorithm (DTC-GA) approach was used to generate the hourly 1 km land-surface temperature (LST) by integrating multi-source satellite data. Diurnal variations of the UHI in ‘ideal’ weather conditions in the city of Beijing were examined. Results show that the DTC-GA approach was applicable for generating the hourly 1 km LSTs. In the summer diurnal cycle, the city experienced a weak UHI effect in the early morning and a significant UHI effect from morning to night. In the diurnal cycles of the other seasons, the city showed transitions between a significant UHI effect and weak UHI or urban heat sink effects. In all diurnal cycles, daytime UHIs varied significantly but night-time UHIs were stable. Heating/cooling rates, surface energy balance, and local land use and land cover contributed to the diurnal variations in UHI. Partial analysis shows that diurnal temperature range had the most significant influence on UHI, while strong negative correlations were found between UHI signature and urban and rural differences in the normalized difference vegetation index, albedo, and normalized difference water index. Different contributions of surface characteristics suggest that various strategies should be used to mitigate the UHI effect in different seasons.     

External and internal attentional environments I. The utilization of cardiac deceleratory and acceleratory response data for evaluating differences in mental workload between machine-paced and self-paced work ∗

Previous evidence has suggested that self-paced (SP) task performance may constitute a higher mental workload than machine-paced (MP) performance. These differences in mental workload were thought to be due to the presence, when working SP, of an internal pacing mechanism serving to maintain the worker's rhythm. In MP tasks, this function would be maintained externally by the machine. The present investigation attempted to directly test this hypothesis. For this purpose, Lacey's psychophysiological model relating changes in heart rate (HR) to attentional demands was employed. Differences in cardiac deceleratory and acceleratory activity between MP and SP performance were evaluated for each of two tasks. In one task, the emphasis was predominantly on visual detection. Based on the suspected direction of attentional demands, this task was characterized as external. The other task required mental solution to arithmetic problems and was categorized accordingly as internal. Psychophysiological findings were consistent with Lacey's basic model and offered no support for the existence of an internal pacing mechanism under SP conditions. Instead, they suggested the presence of uncertainty factors reflecting higher mental workload during the MP performance of both tasks. Performance data, however, did not support the causal interpretation given by Lacey for his psychophysiological model, and were explained in terms of a complex interplay between HR level and HR change.     

Auditory attention and multiattribute decision-making during a 33 h sleep-deprivation period: mean performance and between-subject dispersions.

One purpose of this study was to compare attention in the evening (22:00 h), in the late night (04:00 h), in the morning (10:00 h) and in the afternoon (16:00 h) during a period of complete wakefulness beginning at 08:00 h with a mean daytime performance without sleep deprivation. Another purpose was to investigate sleep deprivation effects on a multi-attribute decision-making task with and without time pressure. Twelve sleep-deprived male students were compared with 12 male non-sleep-deprived students. Both groups were tested five times with an auditory attention and a symbol coding task. Significant declines (p < 0.05) in mean level of performance on the auditory attention task were found at 04:00, 10:00 and 16:00 h for subjects forced to the vigil. However, the effect of the sleep deprivation manifested itself even more in increased between-subject dispersions. There were no differences between time pressure and no time pressure on the decision-making task and no significant differences between sleep-deprived and non-sleep-deprived subjects in decision strategies. In fact, the pattern of decision strategies among the sleep-deprived subject was more similar to a pattern of decision strategies typical for non-stressful conditions than the pattern of decision strategies among the non-sleep-deprived subjects. This result may have been due to the fact that the sleep loss acted as a dearouser. Here too, however, the variances differed significantly among sleep-deprived and non-sleep-deprived subjects, indicating that the sleep-deprived subjects were more variable in their decision strategy pattern than the control group.     

Circadian Rhythms of Food Intake and Oral Temperature in ‘Morning’ and ‘ Evening’ Groups of Individuals

The most marked ‘ morning ’ and ‘evening ’ types in a psychology class were identified by means of a questionnaire, and asked to record their oral temperatures and food intakes throughout the day during a 4-week and a 4-day period respectively. The morning group had its mean circadian temperature maximum 5 h earlier than the evening group, and had its cumulative food intake distribution curve 1¾ h ahead of the evening group. After adjusting the food distributions by 1¾ h in the time base to get a least-square fit, significant differences between the distributions remained. It is suggested that morning types have a more autonomous 24-hour-periodicity than evening types. It is concluded that the questionnaires have the power to discriminate extreme morning and evening types of individuals in terms of oral temperature and food intake. Food intake seems to be a sensitive enough measure to be included in studies of inter-individual differences of circadian rhythms.     

Task performance in heat: a review

A wide array of variable conditions, tasks, subject populations, etc., have been included in studies that have produced data on perceptual motor performance in the heat. This paper uses a methodology for comparing these studies, regardless of the inherent differences, which allows determination of whether thermal effects are dominant enough to persist through diverse combinations of variables. Approximately 160 individual studies of perceptual motor performance reported in the literature were summarized based on thermal level, duration of exposure and the type of task performed. Results indicated no dominant effect of duration of exposure to the heat and no dominant effect of thermal level on mental/cognitive tasks. For perceptual motor tasks other than very simple or mental tasks, an onset of performance decrement was noted in the 30-33°C WBGT range of temperature. This temperature level is consistent with the Recommended Exposure Limits for work in the heat at low levels of metabolic heat.     

The effects of lunch on cognitive vigilance tasks

An experiment was carried out to investigate the effects of lunch on cognitive vigilance tasks. Subjects who ate lunch prior to testing detected fewer targets in a paced, successive comparison task, but did not show impaired performance on a proportion perception task. The experiment also demonstrated some differences between morning and afternoon performance in subjects who abstained from eating lunch. This shows that performance changes observed in the early afternoon may be attributed to at least two components. The first of these is meal-dependent, whereas the second is endogenous, and occurs even when lunch is not consumed.     

Sleepiness in long distance truck driving: an ambulatory EEG study of night driving

Eighteen truck drivers had their EEG recorded continuously during a night or evening drive between southern Sweden and Stockholm (500 km). They also carried out self ratings of sleepiness and performance every hour. The EEG was subjected to spectral analysis. The drivers were divided into two groups with a night group (n = 7) who drove between 20:30 to 07:20, and an evening group (n = 11) who drove between 18:20 and 04:00. The night group showed higher subjective sleepiness and lower subjective performance, and increased alpha and theta burst activity during the last three hours of the drive. The groups did not differ for the first 2-3?h of the drive. For the night group, a significant intraindividual correlation was found between subjective sleepiness and EEG alpha burst activity. End-of-the-drive subjective sleepiness and alpha burst activity were significantly correlated with total work hours and arrival time but not with age, diurnal type, prior (rated) sleep length, total break time, drive time or prior time awake. A regression analysis showed that total work hours and total break time predicted 66% of the variance of alpha burst activity during the end of the drive.     

Tolerance to Shift of Sleep,as Related to the Individual's Circadian Phase Position

The differential adaptation of ‘morning’ and ‘evening’ types to changes in sleep schedules was investigated in two studies. The first was carried out on six female subjects, classified as morning or evening types on the basis of their rhythms of body temperature, and on their answers to a morningness-eveningness questionnaire. Bed times on single nights were varied between 2100h and 0300 h. On each night measurements were taken of latency of sleep onset and of sleep duration. Body temperature, heart rate and respiratory rate were also recorded, as was self-estimated vigilance during the day following the experimental sleep. Evidence of sleep deficiency after late bed limes was found in the morning but not in the evening types; the latter, however, had longer sleep latencies after early bed times than the morning types.

In the second study eight male subjects underwent the same basic experimental treatment, but in this case sleep was monitored for three consecutive nights with a given bed time, in order to examine adaptive processes. The overall results were similar to those of the first study. However, it was also found that, whereas the duration of sleep tended to increase over the three consecutive nights with later bed times in all subjects, this was more marked in the evening than in the morning types.     

Development and application of an algorithm for the estimation of mixing height with the use of a SODAR-RASS remote sensing system

This work introduces a newly developed algorithm for the estimation of mixing height with the use of a SODAR-RASS system (sound detection and ranging; radio acoustic sounding system) and in-situ instrumentation. The algorithm utilizes the temperature, acoustic back-scattered signal and the Richardson number profiles, estimated by the remote sensing system, and incorporates information on the basic meteorological parameters related to the surface flow given by in-situ measurements. It was applied to a two-year period (2007–2008) data set of a SODAR-RASS installed in the Messogia Plain, a coastal region of the eastern Mediterranean Sea. The profiles of the parameters used by the algorithm showed good agreement among the different criteria used for various atmospheric conditions. The mixing height estimates are analysed with respect to the cold and warm seasons of the two-year period, and the frequency distributions of the estimated 30-min mixing height values from the entire time series show clear peaks, associated with certain synoptic or meso-scale phenomena observed over the area. The mean diurnal cycle of the mixing height during the warm period exhibited higher daytime values compared with the corresponding values during the cold period. The dominating synoptic and meso-scale phenomena over the area were analysed, and selected plots of mixing height estimates together with time–height distributions of SODAR-RASS parameters are given. Mixing height values during the evolution of low-level jets show weak diurnal variability, following the lift or the descent of the core of the jet, and in most cases mixing height estimates nearly coincided with the height of the jet's core, while night-time values were kept high due to the increased mixing. For the case of frontal passages, the mixing height follows the intense wind shift line, with values close to the temperature inversion height that separates the two air masses. Under sea–land breeze conditions, mixing height obtains low daytime values due to the elevated inversion that is formed at the upper part of the lower current of the sea breeze cell. The algorithm exhibited unsatisfactory performance during the transition periods (early morning and night-time hours – neutral conditions) of the diurnal cycle.     

Psychophysiological changes during a VDU repetitive task

Abstract

A simulated realistic data-entry task on a visual display unit (VDU) was employed to study the relationships between performance and various physiological indices of arousal. After several training sessions on separate days, subjects performed the data-entry task which lasted 120 min. All the components of the workplace were adjusted in order to provide each subject with suitable ergonomic conditions. Performance (correct entries, errors, omissions) and physiological parameters (spectral analysis of the electroencephalogram (EEG) and heart rate (HR)) were recorded continuously. Three functional tests were performed before and after the data-entry task: an eye muscle balance test, a visual reaction time task (RT) and an attentional-perceptual task (AP) displayed on the terminal. Data-entry task performance showed a progressive decline, reaching minimal values after 45-60 min of work, followed by a significant rebound. This pattern characterized 80% of the subjects and was not dependent on the individual average level of performance. Behavioural responses were found to be associated with corresponding EEG arousal changes: i.e. with a parallel trend of beta activity and an opposite one of theta and alpha activities, whereas average HR decreased from the beginning to the end. There is some evidence that different EEG frequency bands are more sensitive to selective attentional requirements than HR which is rather related to diffuse arousal changes. The before/after tests showed a more pronounced esophoria, an increase of RT and of errors percentage in the AP task after 2 hours of work. The EEG did not show any significant difference after work but the average HR level was significantly lower compared with the before-work values. The EEG pattern accompanying the rebound of the performance during the data-entry task supports the auto-arousal hypothesis which assumes that a cerebral compensatory effort intervenes in a mental repetitive task.     

The impact of free-time activities on sleep, recovery and well-being

We compared the effects of different types of free-time activity on subjective and objective indices of sleep, recovery and well-being in an experimental field study. Twelve participants spent four consecutive evenings after work in each of three conditions: pursuing quiet leisure activities at home; undertaking active leisure pursuits; doing additional work. Ratings of rest and recuperation, and of satisfaction, were lowest in the additional work condition. There were few other differences between conditions. However, being satisfied with one's evening activities (regardless of which experimental condition was being undertaken) was associated with improved subsequent sleep (self-reported). Evening activities involving lower mental effort were also associated with better-rated sleep, as well as improved recuperation and fatigue the next day. It is concluded that the nature of activity per se may be less important than (1) whether the activity accords with individual preference and (2) the cumulative demands of daytime and evening activities.     

Sleep schedules and peak times of oral temperature and alertness in morning and evening ‘types’

Abstract

The relation between circadian variables (oral temperature and subjective alertness) and sleep-awake schedules was explored as a function of a subjective preference index (Home and Ostberg 1976) which classifies subjects as ’morning’ or ‘evening’ type. Measurements of oral temperature and self-assessed alertness were obtained every 3 hours from rising time to bedtime over a 2 week period in 49 medical students. Sleep logs were kept by the students during the same period. Sleep schedules and alertness peak time, as well as the relative temporal location of alertness peak time and temperature peak time, differed in relation to the Home and Ostberg index. These results suggest that in normal conditions the coupling between temperature circadian rhythm and sleep-awake cycle differs in morning types and evening types.     

Circadian changes in resting heart rate and body temperature,maximal oxygen consumption and perceived exertion

To investigate the existence, magnitude and interplay of rhythmic 24-hour variations in human functions, maximal O₂ uptake (VO₂max), resting heart rate (?_H), body temperature (T_b) and rated perceived exertion (RPE) during exercise were measured twice every 2hours over a full day-night cycle. Thirty-one subjects were randomly administered a treadmill test on 24 separate occasions, 48 hours apart. RPE was observed at heart rates of 130, 150 and 170beats/min. Resting T _b, and/H were lower (p< 005) in the morning than afternoon or evening. Measurement of [Vdot]O₂ max revealed no significant differences throughout 24 hours. RPE was higher (p< 0-05)at 130, 150 and 170HR at 02.00 and 04.00hours than at 20.00, 22.00 and 24.00 hours. T _b and ?_H were apparently in phase.and show a sine wave pattern when expressed on a 24-hour scale. These data demonstrate the significance of the circadian variation for the application of functional tests.     

Fighter pilots’ heart rate,heart rate variation and performance during instrument approaches

Fighter pilots’ heart rate (HR), heart rate variation (HRV) and performance during instrument approaches were examined. The subjects were required to fly instrument approaches in a high-fidelity simulator under various levels of task demand. The task demand was manipulated by increasing the load on the subjects by reducing the range at which they commenced the approach. HR and the time domain components of HRV were used as measures of pilot mental workload (PMWL). The findings of this study indicate that HR and HRV are sensitive to varying task demands. HR and HRV were able to distinguish the level of PMWL after which the subjects were no longer able to cope with the increasing task demands and their instrument landing system performance fell to a sub-standard level. The major finding was the HR/HRV’s ability to differentiate the sub-standard performance approaches from the high-performance approaches.

Practitioner Summary:

This paper examined if HR and HRV were sensitive to varying task demands in a fighter aviation environment and if these measures were related to variations in pilot’s performance.     

Validation and application of MODIS-derived SST in the South China Sea

Using a variety of in situ sea surface temperature (SST) data sets in the South China Sea, we validate the satellite-derived SST from the Moderate Resolution Imaging Spectroradiometer (MODIS). Analysis of a large number of match-up samples during 2008–2012 shows that the MODIS SSTs have biases ranging from –0.19°C to –0.34°C and standard deviation (STD) errors ranging from 0.58°C to 0.68°C. Specifically, mean biases are all negative but there are smaller cool biases in daytime than those in night-time. The monthly validation analysis shows that the biases exhibit apparent seasonal variations. The biases in daytime have relatively small magnitudes in spring and summer, while the negative biases in night-time are most apparent in summer. On the other hand, the time series of MODIS SSTs may exhibit an evident diurnal variation for some months, which roughly agrees with the in situ SST measurements. This study also highlights that the MODIS SSTs under cloud-free conditions are effective at detecting the high-frequency and small-scale oceanic features, such as the localized diurnal variation, oceanic front, and coastal upwelling.     

The influence of mental load on muscle tension

We examined the differences in muscle tension and in physiological measures depending on the type of mental task. Fifteen participants performed tests for sustained attention, vigilance and maintaining posture only. We analysed electromyogram (EMG) measures of extensor digitorum (ED), flexor carpi ulnaris (FU), deltoideus (DE) and trapezius (TR), and heart rate (HR) and respiratory frequency (RF). Measures indicated higher values for mental tasks than for maintained posture only with significant differences in all measures. The following relationships were also significant: between DE and physiological measures (HR and RF), between ED and the amplitude of EMG of the other three muscles, between FU and TR and between HR and RF. The results of this study showed that the relationship between mental demands and muscle tension was mostly reflected by tension in the arm and shoulder girdle muscles and, to a lesser degree, in forearm muscles.

Practitioner Summary: We focused on physiological and muscle tension measures differentiating work according to the level of mental demands. Differences in sustained attention, vigilance and maintaining posture only proved that mental demands were mostly reflected by tension in arm and shoulder girdle muscles and, to a lesser degree, in forearm muscles.     

Dual-task performance in multimodal human-computer interaction: a psychophysiological perspective

This paper examines the psychophysiological effects of mental workload in single-task and dual-task human-computer interaction. A mental arithmetic task and a manual error correction task were performed both separately and concurrently on a computer using verbal and haptic input devices. Heart rate, skin conductance, respiration and peripheral skin temperature were recorded in addition to objective performance measures and self-report questionnaires. Analysis of psychophysiological responses found significant changes from baseline for both single-task and dual-task conditions. There were also significant psychophysiological differences between the mental arithmetic task and the manual error correction task, but no differences in questionnaire results. Additionally, there was no significant psychophysiological difference between performing only the mental arithmetic task and performing both tasks at once. These findings suggest that psychophysiological measures respond differently to different types of tasks and that they do not always agree with performance or with participants’ subjective feelings.     

The impact of knowledge representation on cognitive‐oriented task performance

This research examines the impact of training style and operator individual differences on the task representation developed, automatized task performance, and controlled task performance. Results indicate that performance on relatively straightforward repetitive tasks usually associated with automatization is influenced by training style and the mental task representation held by operators. Also, domain representation is a significant determinant of performance on complex cognitive‐oriented tasks requiring controlled processes. Therefore, the task representation is identified as a high‐level performance determinant for both simple and complex task performance. No effect for training style or individual differences was found. It is concluded that training programs for systems requiring human‐computer interaction must account for this factor in order to facilitate the learning process and enhance task performance.     

Physical and thermal strain of firefighters according to the firefighting tactics used to suppress wildfires

The aim of this study was to analyse the physiological strain of firefighters, using heart rate (HR) and core temperature, during real wildfire suppression according to the type of attack performed (direct, indirect or mixed). Three intensity zones were established according to the HR corresponding to the ventilatory threshold (VT) and respiratory compensation threshold (RCT): zone 1, RCT. The exercise workload (training impulse (TRIMP)), the physiological strain index (PSI) and the cumulative heat strain index(CHSI) were calculated using the time spent in each zone, and the HR and core temperature, respectively. Significantly higher mean HR, time spent in Z2 and Z3 and TRIMP h(-1) were found in direct and mixed versus indirect attacks. The highest PSI and CHSI were observed in the direct attack. In conclusion, exercise strain and combined thermal strain, but not core temperature during wildfire suppression, are related to the type of attack performed. STATEMENT OF RELEVANCE: Our findings demonstrated that wildfire firefighting is associated with high physiological demands, which vary significantly depending on the tactics chosen for performing the task. These results should be kept in mind when planning programmes to improve wildland firefighters' physical fitness, which will allow improvement in their performance.     

Field Studies of Shiftwork: I. Temporal Patterns in Psychophysiological Activation in Permanent Night Workers

Abstract

The diurnal variation in body temperature, catecholamine excretion, performance, and subjective alertness was studied among 24 permanent night workers during the 1st, 3rd, and 5th day of their work ‘ week ’of six nights. Most of the variables showed a significant diurnal pattern with high values during work. Furthermore, the patterns of variation were similar during the three nights of measurement without any observable adjustment over the week. It was therefore suggested that permanent night work might facilitate a more rapid switch over to night work after free days.