Released less than a year back by Optech, the Gemini Airborne Laser Terrain Mapping (ALTM) system is a multi pulse system. It has the ability to operate at 167 kHz pulse repetition frequencies. Which means that one can get high pulse rates even from high altitudes. Higher pulse rates = more measured points on the terrain = higher accuracy in the terrain as well as extracted features.
The importance of the purchase for GeoEye is
MJ Harden is now able to merge imagery from their current digital mapping camera with LiDAR imagery to produce enhanced products ideally suited for large-scale mapping projects, such as mapping flood plains, coastal zones and public right of ways and corridors. This is especially important in the pipeline, oil and gas, mining, urban planning, disaster management, and utility and telecommunications industries.
Here are more specs about the Gemini 167 system: http://www.optech.ca/pdf/Gemini167.pdf
The important features in my opinion about this ALTM system - as far as feature extraction go are:
Laser repetition rate 33 - 167 kHz : Lower point spacing/Higher points per square area means more definition in data which in turn allows for extraction and modeling of smaller features on the terrain.
Operating altitude 80 to 4,000 m (higher altitude optional) : Ability to operate at higher altitudes is important especially in hostile environments (Army) and the ability to operate a low altitudes is important for power line corridors as well as capturing dense urban environments.
Horizontal accuracy 1/11,000 x altitude; ±1-sigma* : More accurate models.
Elevation accuracy 5 - 10 cm typical; ±1-sigma : More accurate models.
Range capture Up to 4 range measurements for each pulse, including last : The more number of measurements possible - the better one can model vegetation - such as forests. Typically in urban environments the multiple measurements don't provide very much of an additional advantage.
Intensity capture 4 intensity readings with 12-bit dynamic range for each measurement: Intensity values can be used to determine target material type, as well as for extraction in Feature Analyst.
Spot distribution Sawtooth, uniform spot spacing across 96% of scan: This is important for reliable feature extraction, as well as uniform accuracy.
Swath width Variable from 0 to 0.93 x altitude (m): More important from a cost perspective as higher swath widths allow for fewer flight lines. Less flight time = less money for the acquisition of the data.
Beam divergence Dual divergence 0.15/0.25 mrad or nominal (1/e full angle) 0.80 mrad: