Update ard-processing-extent.md

Update to include nonstandard ancillary comparison with mainland

docs/guides/reference/ard-processing-extent.md

@@ -1,15 +1,15 @@
 # DEA ARD processing extent
 
-DEA produces surface reflectance products from Landsat and Sentinel-2 satellite observations which cover the continent and some near-shore islands of Australia. This data is used to produce derivative products such as DEA Coastlines, Water Observations, and Fractional Cover.
+DEA produces surface reflectance products from Landsat and Sentinel-2 satellite observations which cover the continent and some near-shore islands of Australia. This data is used to produce derivative products such as DEA Coastlines, Water Observations, and Fractional Cover. 
 
 We are extending our baseline satellite data coverage to include Christmas Island, Cocos (Keeling) Islands, Coral Sea Islands, Heard and McDonald Islands, Norfolk Island, and islands in the Torres Strait. Additionally, we are processing imagery over shallow ocean areas to support bathymetry and oceanographic science.
 
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 The new data was requested by and will support Indigenous communities in the Torres Strait, in addition to Government agencies who seek to report on Ocean Ecosystem Accounts and manage the full extent of our Marine Parks.
 
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 The update will support the expansion of [DEA's Summary Product Grid](https://knowledge.dea.ga.gov.au/guides/reference/collection_3_summary_grid/), including a shift in the origin point to the south-west of its current position. The expanded Area of Interest will support several DEA product releases and version updates throughout 2024.
 
+The standard ancillaries used to generate surface reflectance products over the mainland are of higher quality than those over extended offshore areas. For a detailed description of the difference, please see the sections below. 
+
 ## List of locations
 
 Here is the new full list of locations that are supported.