## 3 Results
### Other LAI Products  
There are a wide range of LAI products available. This section discusses some of the widely used LAI products that were operational after 2010. Advancements in radiative transfer models facilitated the development of operational global and regional LAI products. Although discrepancies between ground LAI data and digital LAI products still remain, improvements in atmospheric correction and radiometric calibrations improved LAI retrieval accuracy of many LAI products. MODIS LAI is one of the most widely used LAI products which is based on the biome specific three-dimensional radiative transfer (3D RT) model. This model uses atmospherically corrected reflectance and a biome map to generate retrievals [36]. The MODIS LAI product is derived from the daily MODIS-Terra data and was available since 2000. Moreover, these data are available daily at 1 km spatial resolution. There are many other LAI products that were developed. The multi-angle imaging spectrometer (MISR) is another LAI product that was used since 2000. This product is based on the same 3D RTM algorithms as the MODIS product, where the difference between MODIS and MISR is that MISR uses combined spectral data directional information collected by MISR. MISR algorithms provide LAI retrieval for 60-90% of the model input data [54]. GEOV2 LAI is another LAI product. This product is a Geoland2/BioPar project. GEOV2 is an improvement of the previous GEOV1 product in terms of continuity. GEOV2 data has less than 1% gaps compared to 20% of missing data/gaps in GEOV1 [55], GEOV2 also provides cleaner data that are less affected by radiometric and geometric noise. The data have been freely available since 2000 at the Copernicus portal ([[https://land.copernicus.eu/](https://land.copernicus.eu/)]([https://land.copernicus.eu/](https://land.copernicus.eu/)), accessed on 14 August 2020). Global Land Surface Satellite (GLASS) LAI dataset was developed by Beijing Normal University and can be accessed at ([[http://www.bnu-datacenter.com](http://www.bnu-datacenter.com)]([http://www.bnu-datacenter.com](http://www.bnu-datacenter.com)), accessed on 14 August 2020). This product has a revisit time of eight days and operated from 1982 to 2012. From 2000 to 2012, the GLASS LAI product was derived using general regression neural networks (GRNNs) from MOD09A1, which is a MODIS land surface reflectance [56]. These data were available at 1 km for the globe. GLOBMAP LAI is long term global LAI product which was developed in 1982 through a fusion of MODIS and historical advanced very high resolution radiometer (AVHRR) data. This product was developed by establishing a simple pixel-to-pixel relationship between MODIS and AVHRR datasets. These data were available at 8 km resolution. EPS LAI is a global LAI product generated from AVHRR sensor on board the MetOp (Meteorological-Operational) satellite constellation. These data are available on a 10-day basis from [[https://landsaf.ipma.pt/en/](https://landsaf.ipma.pt/en/)]([https://landsaf.ipma.pt/en/](https://landsaf.ipma.pt/en/)), accessed on 14 August 2020. EPS LAI data are derived from an algorithm that uses the PROSAIL radiative transfer model as input and training data. PROBA-V LAI is a first version Copernicus Global Land service global LAI product available at [[https://land.copernicus.eu/](https://land.copernicus.eu/)]([https://land.copernicus.eu/](https://land.copernicus.eu/)), accessed on 14 August 2020. This dataset is generated from Sentinel-3/OLCI, PROBAV sensors every five days and the spatial resolution of this dataset is 1/3 km. The visible infrared imaging radiometer suite (VIIRS) LAI dataset is a National Aeronautics and Space Administration (NASA) product. This dataset was developed in 2018 and is still operational. The data can be downloaded at [[https://search.earthdata.nasa.gov/search](https://search.earthdata.nasa.gov/search)]([https://search.earthdata.nasa.gov/search](https://search.earthdata.nasa.gov/search)), accessed on 14 August 2020.