, 2013). In the same general location, Silliman et al.’s (2012) comparative observations of abnormal levels of total polyaromatic hydrocarbons (PAHs) in sediment samples collected in October 2010 at 3 m and 15 m from the waters’ edge indicated that MC-252 oil from the DWH spill had reached some nearshore marshes. The implication of the previous reported results is that all observational sources including visual, optical, and PolSAR identified heavily oiled and structurally damaged shoreline marshes. In contrast, only the L-band PolSAR enabled detection of low oil contamination in nearshore and interior marsh canopies

that did not exhibit visual structural PI3K Inhibitor Library nmr damage or manifest health impairment at canopy top. However, the lack of direct observational evidence prevents an absolute determination of whether UAVSAR-derived products detected oil exposure in interior marshes. The objective of the research described herein was to confirm whether the spatial distribution of MC-252 oil determined from ground validation corroborated the PolSAR backscatter indicator of oil extent; mainly, did MC-252 oil reach further into the marshlands, as indicated by PolSAR backscatter, than the shoreline check details oiling detected in visual and optical

surveys? It is important to note that the marshlands of Barataria Bay, as with all the southern Louisiana marshes, are subject to historic oiling from other sources. PolSAR is not sensitive to the type of oil that is being detected; thus, to merely show that there was oil in the near-shore and interior marshes, although necessary, would not be sufficient to prove that oil was likely to have been present when the PolSAR data were collected not after the DWH spill in 2010.

In order to confirm that MC-252 oil reached the interior marshes in northeastern Barataria Bay, Louisiana where substantial changes in the 2010 PolSAR backscatter occurred, it was imperative that the oil detected be unambiguously linked to MC-252 oil from the DWH. We accomplished this through oil source-fingerprinting of sediment samples collected in June 2011 at focused locations of observed shoreline oiling and nearshore and interior marsh sites that exhibited substantial change in the 2009 pre-spill and 2010 post-spill backscatter mechanism. Samples were also collected from sites with no substantial change for comparison. Tying the oil to the 2010 spill was critical to showing that L-band PolSAR is a legitimate method for detecting subcanopy oiling. A total of 29 sediment samples were collected at locations selected based on the UAVSAR data and in-situ field observations made in June 2011. No similar conditions of extensive oil slicks and elevated sea levels occurred after the 2010 UAVSAR PolSAR collection to the time of the marsh sediment collections one year later.