Some very broad definitions go something like \u2018remote sensing<\/a> is studying something without touching it\u2019. While true in the most basic sense of the words, such definitions aren\u2019t really very useful. Without going into philosophical<\/a> discussions about what \u2018studying\u2019 and \u2018touching\u2019 mean anyways, I think we can agree that you are not doing remote sensing right now as you are reading this document on a computer screen\u2026 despite learning what this document says without touching it. More appropriately for this course, we can define remote sensing as using an instrument (the sensor) to collect information about the Earth\u2019s surface (or other parts of the Earth, its oceans or atmosphere, or other planets for that matter) at large extents and at some distance. Typical examples include use of satellite imagery or aerial photography, but acoustic sensing (e.g. of the seafloor) and other technologies that do not create data in the form of an \u2018image\u2019 are also part of the broad subject of remote sensing. This kind of definition means that another term, \u2018Earth Observation\u2019, is often used interchangeably with \u2018remote sensing\u2019.<\/p>\n Passive sensing <\/strong><\/p>\n There are many ways to split existing remote sensing technologies up into categories. Some technologies rely on ambient energy (e.g. energy that is naturally present in the environment, such as sunlight). These are called passive sensing technologies<\/a>.<\/p>\n Active sensing<\/strong><\/p>\n Others provide their own source of energy, emitting an energy pulse toward a target area and recording the part of it that is reflected back to the sensor (think about the sonar used on submarines<\/a>). These are called active sensing technologies.<\/p>\n Optical sensing <\/strong><\/p>\n Another way to categorize remote sensing technologies is by the kind of energy they use. Some technologies rely on visible light (e.g. traditional aerial photography), while other technologies expand the range of wavelengths sensed to the ultraviolet and infrared (which is also the kind of \u2018light\u2019 your TV\u2019s remote control uses). When measuring reflected sunlight in these wavelengths, these are called passive optical sensing technologies \u2013 optical because the instruments employ classic optics in their design. The satellite images seen on Google Earth, or used as a background on televised weather forecasts, are images created with passive optical remote sensing. A form of active optical sensing is called lidar, light detection and ranging. It involves emitting a laser pulse (the active part) toward a target and measuring the time it takes before that pulse has hit something and part of it returns to be measured at the sensor. The intensity of the return pulse is typically also measured.<\/p>\n","protected":false},"excerpt":{"rendered":"Review of remote sensing technologies<\/h3>\n