A vast number of studies examined the effects of environmental noise on sleep, and there are different methods to measure sleep.

1. The most comprehensive methodology to physiologically assess sleep is so-called polysomnography (PSG), which encompasses various measurements, including electrophysiological assessment of brain activity (electroencephalogram, EEG), eye movement (electrooculogram, EOG), heart activity (electrocardiogram, ECG), as well as muscle activity (electromyogram, EMG).

^{Figure 1: Schematic representation of the electrode positioning for the measurement of polysomnography (source: DLR)
Figure 2: Preparing subjects for polysomnographic recordings (source: DLR)}

2. A less invasive method for participants is actigraphy, which measures a person's body movements via a single device worn on the wrist. In recent studies, authors attempted to use the combination of actigraphy and ECG measurements in order to detect awakenings in a less costly way than employing PSG.

3. Next to physiological measurements, there is also the option to ask participants about their experience of sleep disturbances or sleep quality, i.e. a psychological assessment of sleep. The items used for this type of assessment can refer to the last night's sleep or a participant's sleep experience over a more extended period. Estimates using questionnaires are relatively cheap and easy to implement. Numerous published examples have been used for calculating 'mean' exposure-response curves of 'at least a little sleep disturbed', 'sleep disturbed' and 'highly sleep disturbed' people over an energy equivalent noise level L_Night. In March 2020, the new Directive EU 2020/367 was published providing the basis for the calculation of the number of highly sleep-disturbed residents depending on the nocturnal aircraft noise level  as well as for the estimation of the total number of people affected by high aircraft noise-induced sleep disturbance. However, research has shown that psychological assessments do not necessarily reflect physiologically measured sleep disturbances and interruptions.

A fundamental problem with exposure response curves based on equivalent levels, is that those 'mean' levels, if not unrealistically low, are not suitable for communication to communities or for protection purposes for noise effects on sleep as many different noise situations can lead to the same L_eq and have different effects on sleep. The World Health Organisation recommends in its "Environmental Noise Guidelines for the European Region" (2018) an L_Night threshold of 40 dB(A) for aircraft noise due to the number of 'Highly Sleep Disturbed people' (HSD), assessed by questionnaires (WHO, 2018). In reality, a Boeing 747 on take-off with a distance of 10 km from the runway, 600 m height, one movement per 8 hours already would lead to an L_Night  of 51 dB(A), or for an Airbus 320, 10 km distance from the runway on take-off, 770 m height, eight movements per 8 hours would lead to an L_Night  of 50 dB(A).

With this information in mind, to develop a night noise protection concept, it seems advisable to revert to (1) physiologically measures sleep assessment techniques and (2) to acoustical parameters of single aircraft noise events, such as maximum levels, event duration, and level rise speed, instead of referring to equivalent levels for the whole night. This technique focuses on the relationship between the acoustic parameters of single noise events during sleep time and reactions in sleep, particularly awakening reactions due to the noise event. This so-called event-related analysis also allows the development of exposure-response models and, thus, estimates the number of additional awakening reactions resulting from aircraft noise events that serves as the basis for night noise protection concepts. Therefore, despite their complex and laborious assessment, the advantages of physiological measurements of sleep disturbances and interruptions against self-assessments become apparent.