# Correction of Directional Effects in VEGETATION NDVI Time-Series
## 2 Vegetation Data Sets  
Top of Atmosphere (TOA) reflectances from the VEGFATION instruments on board SPOT-4 ([[https://earth.esa.int/web/guest/missions/3](https://earth.esa.int/web/guest/missions/3) rd-party-missions/current-missions/spot-4]([https://earth.esa.int/web/guest/missions/3](https://earth.esa.int/web/guest/missions/3) rd-party-missions/current-missions/spot-4), accessed on 15 March 2021) (VGT1: March 1998-July 2003), SPOT-5 ([[https://earth.esa.int/web/eoportal/satellite-missions/s/spot-5](https://earth.esa.int/web/eoportal/satellite-missions/s/spot-5)]([https://earth.esa.int/web/eoportal/satellite-missions/s/spot-5](https://earth.esa.int/web/eoportal/satellite-missions/s/spot-5)), accessed on 15 March 2021) (VGT2: May 2002-May 2014) and PROBA-V ([[http://proba-v.vgt.vito.be/en/about/proba-v-satellite-mission](http://proba-v.vgt.vito.be/en/about/proba-v-satellite-mission)]([http://proba-v.vgt.vito.be/en/about/proba-v-satellite-mission](http://proba-v.vgt.vito.be/en/about/proba-v-satellite-mission)), accessed on 15 March 2021) (VGTPV: October 2013-June 2020) satellites yield the useful input to compute a long-term BRDF-adjusted NDVI Time-Series. Land surface reflectances at 1 km with almost daily global coverage were obtained from the VEGFATION instruments. Satellite scenes images at 333 m and 100 m spatial resolution are acquired by the VGTPVinstrument, albeit with less coverage for the second one (for a full description of the VGTPV instrument see [7]). The VEGETATION instrument is equipped of four wide spectral bands (BLUE, RED, NIR and SWIR) with only two considered here (see Table 1).  
VGT1 and VGT2 TOA reflectances used in this processor are the standard VGT-P Collection 3 [18] products provided by the SPOT/VEGFATION program through the VITO Product Distribution Facility ([[http://www.vito-eodata.be/](http://www.vito-eodata.be/)]([http://www.vito-eodata.be/](http://www.vito-eodata.be/)) accessed on 15 March 2021). VGTPV TOA reflectances are the Collection 1 Level2A 1 km products issued from the PROBA-V nominal processing chain. The PROBA-V product user manual [19] ([[http://proba-v.vgt.vito.be/sites/proba-v.vgt.vito.be/files/products_user_manual.pdf](http://proba-v.vgt.vito.be/sites/proba-v.vgt.vito.be/files/products_user_manual.pdf)]([http://proba-v.vgt.vito.be/sites/proba-v.vgt.vito.be/files/products_user_manual.pdf](http://proba-v.vgt.vito.be/sites/proba-v.vgt.vito.be/files/products_user_manual.pdf)) accessed on 15 March 2021) contains a full description of TOA reflectances measured by VGTPV.  
A subdataset of the NDVI 1 km V2 product serves to illustrate the performance of the BRDF correction (see Section 4). As aforementioned, NDVI 1 km V2 product inputs are VGT1, VGT2 and VGTPV RED and NIR 1 km 10-days synthesis (using a Maximum Value Composite approach) of atmospherically corrected reflectance data sets. Please note that a spectral correction is applied only to the NDVI derived from VGT1. A full description of the Copernicus Global Land Service NDVI 1 km V2 product, hereafter referred to as NDVI MVC, can be found in the Algorithm Theoretical Basis Document (ATBD) [20] ([[https://land.copernicus.eu/global/sites/cgls.vito.be/files/products/GIOGL1_PUM_NDVI1](https://land.copernicus.eu/global/sites/cgls.vito.be/files/products/GIOGL1_PUM_NDVI1) km-V2_2_I2.31.pdf]([https://land.copernicus.eu/global/sites/cgls.vito.be/files/products/GIOGL1_PUM_NDVI1](https://land.copernicus.eu/global/sites/cgls.vito.be/files/products/GIOGL1_PUM_NDVI1) km-V2_2_I2.31.pdf) accessed on 15 March 2021).