Deforestation in the Brazilian Amazon fell by more than a fifth for the 12-month period ending July 31, 2012, according to preliminary data released by Brazil's National Institute for Space Research (INPE). INPE's Real Time Deforestation Detection System (DETER), picked up 2011 square kilometers of forest clearing between August 1, 2011 and July 31, 2012. In the year-earlier period, deforestation amounted to 2,578 sq km. DETER is based on relatively coarse satellite imagery, using 25 hectare pixels from NASA's MODIS sensor. Since the system misses a significant proportion of deforestation, Brazil relies on PRODES (Program to Calculate Deforestation in the Amazon), which can detect areas of deforestation of more than 6.5 hectares, to make the final determination of deforestation on a year-to-year basis, usually releasing estimates each December. INPE cautions that DETER data should not be used to estimate annual rates of deforestation.