Description: Remote sensing of night light emissions in the visible band offers a unique opportunity to directly observe human activity from space. This has allowed a host of applications including mapping urban areas, estimating population and GDP, monitoring disasters and conflicts. More recently, remotely sensed night lights data have found use in understanding the environmental impacts of light emissions (light pollution), including their impacts on human health. In this review, we outline the historical development of night-time optical sensors up to the current state of the art sensors, highlight various applications of night light data, discuss the special challenges associated with remote sensing of night lights with a focus on the limitations of current sensors, and provide an outlook for the future of remote sensing of night lights. While the paper mainly focuses on space borne remote sensing, ground based sensing of night-time brightness for studies on astronomical and ecological light pollution, as well as for calibration and validation of space borne data, are also discussed. Although the development of night light sensors lags behind day-time sensors, we demonstrate that the field is in a stage of rapid development. The worldwide transition to LED lights poses a particular challenge for remote sensing of night lights, and strongly highlights the need for a new generation of space borne night lights instruments. This work shows that future sensors are needed to monitor temporal changes during the night (for example from a geostationary platform or constellation of satellites), and to better understand the angular patterns of light emission (roughly analogous to the BRDF in daylight sensing). Perhaps most importantly, we make the case that higher spatial resolution and multispectral sensors covering the range from blue to NIR are needed to more effectively identify lighting technologies, map urban functions, and monitor energy use.

Description: A revision is made of the genera Hypnodendron and Braithwaitea. Mniodendron and Sciadocladus are reduced to Hypnodendron, Limbella is excluded from the Hypnodendraceae, and Dendro-Hypnum is considered to be not validly published. Hypnodendron rigidum Mitt. is transferred to Pterobryella. The species of Hypnodendron are grouped into nine sections. Five of these are monotypic, viz. Leiocarpos Dix. and four new ones: Lindbergiodendron (including H. arcuatum), Tristichophyllum (H. diversifolium), Mniodendropsis (H. milnei), and Pseudomniodendron (H. fusco-mucronatum). The circumscription of the family also needs revision, but has been maintained unchanged for the time being in the absence of information regarding assumedly related families.\nA number of morphological and other characters are discussed. Hypnodendron is thought to be of pleurocarpous descent; Meusel\xe2\x80\x99s derivation of the growth-form of Hypnodendron from that of the acrocarpous genera Mnium and Philonotis is rejected. Rejuvenation takes place by means of basal innovations, and in a number of erect species also by distal ones. The umbellate and palmate fronds are assumed to have been derived from a pinnate type. The Hypnodendraceae are distributed in the Indo-Pacific and Australasian regions and in southern South America. Hypnodendron is centred in Melanesia and New Zealand. 26 species are recognized, 9 of which are divided into subspecies or varieties; 5 taxa are reinstated (H. colensoi, H. comatum, H. comosum var. sieberi, H. spininervium ssp. spininervium and ssp. archeri) and 1 is described as new (H. vitiense ssp. australe). Identification keys are provided, and for each taxon are given: synonymy together with pertinent literature and typification, misinterpretations and misidentifications, description, geographical distribution, ecology, and notes on various subjects. Each species is illustrated, and a list is given of specimens examined, mostly accompanied by a distribution map.