# Mapping with Pleiades--End-to-End Workflow
### The Pleiades Satellite System  
The European Pleiades satellite system is a dual system comprising the two identical satellites Pleiades-1A and Pleiades-1B. They have been launched in December 2011 and in December 2012, respectively, both providing VHR image data (where VHR is defined for resolutions or ground sampling distances (GSD) below 1 m [28]). The satellites operate in the same orbit with an offset of 180 degrees to offer a daily revisit capacity. They also share the same orbit as the satellites Spot-6 and Spot-7 but are positioned 90 degrees phase shifted. They are supplied with remarkable agility, as the pointing angles can be triggered in a range of \(\pm\)47 degrees (standard mode \(\pm\)30 degrees). The sensors are capable of acquiring a panchromatic band (470-830 nm) with 0.7 m GSD at nadir and four multi-spectral bands (blue: 430-550 nm; green: 500-620 nm; red: 590-710 nm; near-infrared: 740-940 nm) with 2.8 m GSD. Images of the Pleiades sensor get delivered as a bundle of a panchromatic band upsampled to 0.5 m GSD and multi-spectral bands at 2.0 m GSD in GeoTIFF or JPEG format. The multi-spectral information can be pansharpenend [29; 30] or, alternatively, a multi-spectral pansharpend product can directly be ordered. The swath width of Pleiades image data is 20 km on ground, that corresponds to 40,000 pixels in across track direction. Interestingly, the Pleiades open star cluster was the best place to steer the eponymous satellite in the calibration phase [31]. For additional information on the Pleiades sensors we refer to References [27; 32; 33; 34; 35].  
The satellite agility is of importance with respect to 3D mapping from Pleiades image data. Similar to the present VHR missions of Ikonos, Spot or WorldView, stereo data can be acquired during one overflight (single pass) through an appropriate forward and backward arrangement of the sensor. A significant innovation and advantage of Pleiades, however, is provided through the capability to acquire even three images for an area, taken from the same orbit at along track forward-, nadir- and backward-view of the sensor and through the possibility of an across track swipe. Such image triplets are also denoted as tri-stereo data sets. An assessment of the benefit of such arrangements was made, for example, in Reference [36], with respect to image triplets composed from multi-sensor and multi-temporal acquisitions, respectively. In addition to that, the Pleiades sensors are also able to steer in across track direction such that they can collect images over the same scene on ground from different orbits yielding also across track stereo pairs. This enables the collection of multiple view geometry data sets (term taken from Reference [37]) as well known from computer vision and photogrammetry. The sensor model is delivered as a rational polynomial coefficient (RPC) model. The geo-location accuracy of this model is reported to be in the order of 8.5 m CE90 [32]. According to Reference [38] CE90 is defined as the radial error which 90% of all errors in a circular distribution will not exceed, that is, the 90 th percentile of circular error distribution. Therefore, for accurate mapping, the geo-location accuracy has to be refined, that is, optimized using GCPs. Additionally, the launch of the Pleiades-Neo satellite constellation is planned between 2020 and 2022 [39]. It consists of four satellites with a panchromatic band at 0.3 m GSD, six spectral bands (deep blue, blue, green, red, red edge, near-infrared) at 1.2 m GSD, a swath width of 14 km, an envisaged geo-location accuracy of 5 m CE90 and a mission lifetime of more than 10 years.