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Data Extent

Data From: Assessing variability of corn and soybean yields in central Iowa using high spatiotemporal resolution multi-satellite imagery

This dataset includes daily two-band Enhanced Vegetation Index (EVI2) at 30-m resolution over a Landsat scene (path 26 and row 31) in central Iowa. Fourteen years of daily EVI2 from 2001 to 2015 (except 2012) were generated through fusing and interpolating Landsat-MODIS data.

Landsat surface reflectances were order and used in this study. Mostly clear Landsat images from each year were chosen to pair with MODIS images acquired from the same day to generate daily Landsat-MODIS surface reflectance using the Spatial and Temporal Adaptive Reflectance Fusion Model (STARFM). Partially clear Landsat images were also used in generating the smoothed and gap-filled daily VI time-series. All available Landsat data including Landsat 5 Thematic Mapper (TM), Landsat 7 Enhanced Thematic Mapper Plus (ETM+) and Landsat 8 Operational Land Imager (OLI) were used in this study.

The MODIS data products were downloaded and processed. These include the daily surface reflectance at both 250m (MOD09GQ) and 500m (MOD09GA) resolution, the MODIS Bidirectional Reflectance Distribution Function (BRDF) parameters at 500m resolution, and the MODIS land cover types at 500m resolution (MCD12Q1). They were used to generated daily nadir BRDF-adjusted reflectance (NBAR) at 250m resolution for fusing with Landsat.

The Landsat-MODIS data fusion results for 2001-2014 were generated from a previous study (Gao et al, 2017; doi: 10.1016/j.rse.2016.11.004). Data fusion results for 2015 were generated using Landsat 8 OLI images from day 194, 226, 258 and 338 in this study. Cloud masks were extracted from Landsat and MODIS QA layers and were used to exclude cloud, cloud shadow and snow pixels. Since Landsat 5 TM operational imaging ended in November 2011 and Landsat 8 OLI has not been launched until February 2013, Landsat 7 ETM+ Scan Line Corrector (SLC)-off images are the only available Landsat data. For this reason, 2012 was not included.

Due to the cloud contamination in the Landsat and MODIS images, the fused Landsat-MODIS results still have invalid values or gaps. To fill these gaps, a modified Savitzky-Golay (SG) filter approach was built and applied to smooth and gap-fill EVI2. The SG filter is a moving fitting approach. Each point is smoothed using the value computed from the polynomial function fit to the observations within the moving window. The program removes spike points if the fitting errors are larger than the predefined threshold (default 3 standard deviation). The modified SG filter allows us to retain small variations but also fill large gaps in an unevenly distributed time-series EVI2.

Daily EVI2 files are saved in one tar file per year. Each tar file contains a binary image file and a text header file that can be displayed in the ENVI software. The binary image file has the dimension of 7201 lines by 8061 samples by 365 days and is saved in BIP (band interleaved by pixel) format. EVI2 data are saved in 4-byte float number. The text header file contains necessary information including projection and geolocation. Daily EVI2 file is named as "flexfit_evi2.026031.yyyy.bin", where "026031" refers to the Landsat path and row, and yyyy represents year and ranges from 2001-2015.

FieldValue
Tags
Modified
2022-06-03
Release Date
2019-10-01
Frequency
Daily
Identifier
4f541166-34d9-4504-9cd7-1275ba52223c
Spatial / Geographical Coverage Area
POLYGON ((-91.368417 43.501391, -91.215062 43.501391, -91.204109 43.353514, -91.056231 43.254929, -91.176724 43.134436, -91.143862 42.909881, -91.067185 42.75105, -90.711184 42.636034, -90.639984 42.510065, -90.420906 42.329326, -90.393521 42.225264, -90.168967 42.126679, -90.141582 42.000709, -90.179921 41.809016, -90.311367 41.743293, -90.344229 41.589939, -90.656414 41.463969, -91.045277 41.414677, -91.111001 41.239415, -90.946692 41.097014, -90.963123 40.921752, -91.09457 40.823167, -91.121954 40.669813, -91.401278 40.560274, -91.417709 40.379535, -91.527248 40.412397, -91.729895 40.615043, -91.833957 40.609566, -93.257961 40.582182, -94.632673 40.571228, -95.7664 40.587659, -95.881416 40.719105, -95.826646 40.976521, -95.925231 41.201076, -95.919754 41.453015, -96.095016 41.540646, -96.122401 41.67757, -96.062155 41.798063, -96.127878 41.973325, -96.264801 42.039048, -96.44554 42.488157, -96.631756 42.707235, -96.544125 42.855112, -96.511264 43.052282, -96.434587 43.123482, -96.560556 43.222067, -96.527695 43.397329, -96.582464 43.479483, -96.451017 43.501391, -91.368417 43.501391))
Publisher
Ag Data Commons
Spatial / Geographical Coverage Location
Central Iowa
Temporal Coverage
January 1, 2001 to December 31, 2015
License
Contact Name
Gao, Feng
Contact Email
Public Access Level
Public
Program Code
005:040 - Department of Agriculture - National Research
Bureau Code
005:18 - Agricultural Research Service