Wrist actigraphy is commonly used to measure sleep, and hip actigraphy is commonly used to measure activity. It is unclear whether hip‐based actigraphy can be used to measure sleep. This study assessed the validity of wrist actigraphy and hip actigraphy compared to polysomnography (PSG) for the measurement of sleep. 108 healthy young adults (22.7 ± 0.2 years) wore hip and wrist GTX3+ Actigraph during overnight PSG. Measurements of total sleep time (TST), sleep efficiency (SE), sleep onset latency (SOL) and wake after sleep onset (WASO) were derived and compared between wrist actigraphy, hip actigraphy and PSG. Sensitivity, specificity and accuracy of wrist actigraphy and hip actigraphy for each variable were derived from epoch‐by‐epoch comparison to PSG. Compared to PSG: TST and SE were similar by wrist actigraphy but overestimated by hip actigraphy (both by 14%); SOL was underestimated by wrist actigraphy and hip actigraphy (by 39 and 80%, respectively); WASO was overestimated by wrist actigraphy and underestimated by hip actigraphy (by 34 and 65%, respectively). Compared to PSG the sensitivity, specificity and accuracy of wrist actigraphy were 90, 46 and 84%, respectively; and of hip actigraphy were 99, 14 and 86%, respectively. This study showed that using existing algorithms, a GTX3+ Actigraph worn on the hip does not provide valid or accurate measures of sleep, mainly due to poor wake detection. Relative to the hip, a wrist worn GTX3+ Actigraph provided more valid measures of sleep, but with only moderate capability to detect periods of wake during the sleep period.

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The Shuttle Radar Topography Mission (SRTM) successfully acquired terrain elevation data for 80 percent of the Earth's landmass in February 2000. The radar system and data collection scheme designed by NASA's Jet Propulsion Laboratory (JPL) met the global requirements of the U.S. Department of Defense for Level 2 Digital Terrain Elevation Data (DTED ®). JPL processed the raw data into unfinished DTED ® 2 and other products that were delivered to two contractors of the National Geospatial-Intelligence Agency. The contractors edited the unfinished DTED ® 2, updated the associated products, and generated finished products for distribution. Automated processes were developed by each contractor to identify, delineate and set heights for lakes, rivers, and ocean coastlines in conformance with an extensive set of editing rules created to maintain consistency and uniformity in the final products. The finished DTED ® is significantly better than the 16 m vertical accuracy required by the original specification.

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Accurate measurement of time at lights out is essential for calculation of several measures of sleep in wrist-activity monitors. While some devices use subjective reporting of time of lights out from a sleep diary, others utilise an automated proprietary scoring algorithm to calculate time at lights out, thereby negating the need for a sleep diary. This study aimed to compare sleep-measures from two such devices to polysomnography (PSG) measures (In-Laboratory) and against each other when worn at home (At-Home). Fifty middle-aged adults from the Raine Study underwent overnight PSG during which they wore an ActiGraph™ and a Readiband™. They also wore both devices at home for 7 nights. The Readiband uses an automated proprietary algorithm to determine time at lights out whereas the ActiGraph requires completion of a sleep diary noting this time. In laboratory, compared to PSG: Readiband underestimated time at lights out, sleep onset, and wake after sleep onset, overestimated sleep latency and duration (p<0.001 for all); while ActiGraph underestimated sleep latency and wake after sleep onset and overestimated sleep efficiency and duration (p<0.001 for all). Similar differences between devices were observed on the laboratory night and when at home. In conclusion, an automated algorithm such as the Readiband may be used in the same capacity as the ActiGraph for the collection of sleep measures including time at sleep onset, sleep duration and time at wake. However, Readiband and ActiGraph measures of sleep latency, efficiency and wake after sleep onset should be interpreted with caution.