Selection and quality assessment of Landsat data for the North American forest dynamics forest history maps of the US

Using the NASA Earth Exchange platform,the North American Forest Dynamics(NAFD)project mapped forest history wall-to-wall,annually for the contiguous US(1986–2010)using the Vegetation Change Tracker algorithm.As with any effort to identify real changes in remotely sensed time-series,data gaps,shifts in seasonality,misregistration,inconsistent radiometry and cloud contamination can be sources of error.We discuss the NAFD image selection and processing stream(NISPS)that was designed to minimize these sources of error.The NISPS image quality assessments highlighted issues with the Landsat archive and metadata including inadequate georegistration,unreliability of the pre-2009 L5 cloud cover assessments algorithm,missing growing-season imagery and paucity of clear views.Assessment maps of Landsat 5–7 image quantities and qualities are presented that offer novel perspectives on the growing-season archive considered for this study.Over 150,000+Landsat images were considered for the NAFD project.Optimally,one high quality cloud-free image in each year or a total of 12,152 images would be used.However,to accommodate data gaps and cloud/shadow contamination 23,338 images were needed.In 220 specific path-row image years no acceptable images were found resulting in data gaps in the annual national map products.

Reductions in productivity due to land degradation in the drylands of the southwestern United States

Dryland degradation has long been recognized at regional,national,and global scales,yet there are no objective assessments of its location and severity.An assessment of reductions in net primary production(NPP)due to dry land degradation in the southwestern United States is reported.The local NPP scaling(LNS)approach was applied to map the extent and magnitude of degrada tion.LNS seeks to identifty reference sites in which there is no degradation that can be used as a standard for comparison with other sites that share the same environment,except for degradation.Twelve years were analyzed(2000--2011),using Normalized Difference Vegetation Index(NDVI)data(250 m)from the Moderate Resolution Imaging Spectroradiometer(MODIS)satellite-borne multispectral sensor.The results indicated that the total NPP reductions in the study area were about35.9±4.7Tg C/yr,which equates to 0.31±0.04 Mg C·ha^(-1)· yr^(-1).The NPP reductions in grassland-savanna and livestock grazing areas were large and mostly consistent between years in spite of large variations in overall NPP caused by differences in land-use,interannual variations in rainfall,and other aspects of weather.In comparison with other cover types,forested land generally had higher NPP reduction per unit area.The maps also enable attribution of degradation from the finest management units to entire agencies,such as the Bureau of Land Management,which had 50%less production per unit area than the U.S.Forest Service.The degradation within Native American land was low with total NPP reduction of about 2.41±0.24 Tg C/yr and unit area reduction of productivity of just 0.21±0.02 Mg C·ha^(-1)·yr^(-1),yet the percent reduction from potential was in equivalence with other land management agencies.