Landsat image series are long-term times series observing the earth’s surface at a relatively fine spatial resolution of 30 m on the visible and infrared channels, which can be used to monitor vegetation dynamics using band ratios such as NDVI. However, due to cloud cover, having Landsat NDVI at a high temporal resolution is impossible. This is especially found in high-humidity regions such as Indonesia, particularly in the rainy season. Whereas some studies, such as long-term phenological observations and detailed land use/land cover change detection, may require Landsat NDVI with a high temporal resolution. One of the higher temporal resolution images with similar spectral characteristics to Landsat is MODIS, which can be used to fill the gap; however, it may have a coarser spatial resolution. Thus, some methods have been developed to blend Landsat and MODIS images to create images with both Landsat spatial detail and MODIS high temporal resolution. Unfortunately, the blending methods are usually not straightforward, where complex steps are required to find and combine several techniques with advanced computational skills. This study, therefore, aims to develop an integrated method to create high temporal Landsat NDVI using free and open-source software (FOSS) GIS application, which is easily accessible and applicable. © 2024 Institute of Physics Publishing. All rights reserved.