Introduction: Permanently shadowed regions (PSRs) near the lunar poles that only receive secondary illumination (reflected from Sun facing slopes) were imaged by the Lunar Reconnaissance Orbiter (LRO) Narrow Angle Cameras (NAC) . Secondary lighting is optimal in polar areas around respective solstices and when the LRO orbit is nearly coincident with the sub-solar point (low spacecraft β-angles). The main goal of PSR imaging is to investigate the distribution of cold-trapped volatiles. The NAC PSR images may record evidence of surface frosts, unusual morphologies from ice rich regolith, and aid in planning potential landing sites for future in-situ exploration.
Secondary illumination imaging in PSRs requires NAC exposure times more than ten times greater than nominal imaging. The increased exposure time results in downtrack smear, which decreases the spatial resolution of the NAC PSR images. Most long exposure NAC images of PSRs were acquired with exposure times of 24.2-ms (1-m by 40-m pixels, sampled to 20-m) and 12-ms (1-m by 20-m, sampled to 10-m).
Polar Campaigns: The north polar campaign ran from February 2013 to April 2013. Relative to the south-polar region, PSRs near the north pole are generally smaller (D<24-km) and located in bowl shaped craters. Long exposure NAC images of PSRs in bowl shape craters were well illuminated by reflected light from crater walls during the northern summer solstice, allowing many PSRs to be imaged with the shorter exposure time of 12-ms (resampled to 10-m). With the exception of some craters in Peary crater, most notable PSRs were successfully imaged.
The third PSR south polar campaign began in April 2013 and will continue until October 2013. The third campaign will expand NAC coverage of PSRs following up on earlier discoveries with new images of higher signal to noise ratio (SNR), higher resolution, and varying secondary illumination conditions. Utilizing previous campaign images, and spacecraft data, an individualized approach for targeting each crater will drive this campaign.
Interior of PSRs: Secondary lighting within the PSRs, though somewhat diffuse, is at low incidence angles and coupled with nadir imaging of the NACs results in large phase angles. Such conditions tend to reduce albedo contrasts complicating identification of patchy frost or ice deposits. Within the long exposure PSR images, few small craters (D<200-m) with highly reflective ejecta blankets were identified and interpreted as small fresh impact craters. Sylvester N and Main L are Copernican-age craters with PSRs; NAC images reveal debris flows, boulders, and morphologically fresh interior walls indicative of their young age. The identifications of albedo anomalies associated with these fresh craters and debris flows indicate that strong albedo contrasts (~2x) can be distinguished in PSRs. Lunar highland material has an albedo of ~0.2, while pure water frost has an albedo of ~0.9. If PSRs have an albedo similar to lunar highlands, significant surface frost deposits could result in detectable reflective anomalies in the NAC images. However, no reflective anomalies have yet been identified in PSRs that can confidentially be attributed to water frost.
 S.D. Koeber and M.S. Robinson (2013)LPSC XLIV,Abstract#2588.