# An Overview of the Applications of Earth Observation Satellite Data: Impacts and Future Trends
## 3 Results  
### Statistical Characteristics  
As shown in Figure 1, the number of publications and citations relevant to EO satellites have both been increasing exponentially, which demonstrates that the application of EO satellites is becoming more and more widespread. As EO technology develops rapidly, the data supplied have ever higher resolutions, and the quantity of data is also increasing exponentially [64; 65; 66]. The use of EO data has gradually been introduced into many different applications [12]. However, the number of papers related to some particular satellites and sensors has decreased in recent years. For example, the number of documents related to AVHRR, SPOT, and TerraSAR currently show a significant decreasing trend. The main reason for this is that the overall upgrading of satellites and sensors and advances in EO technology have led to other types of more advanced satellite data becoming available. It is noted that long time-series EO satellite data are still valuable for the remote sensing community. Consistent and effective long-term observations are needed to promote the value of EO satellite data, which is why satellite missions launch new satellites continually. For example, Landsat 9 was successfully launched on 27 September 2021, which is expected to observe Earth for five years and continue the Landsat missions until 2026. It is also clear that the application of EO data is highly concentrated on data from a small number of satellites and sensors: there have been far more applications of Landsat and MODIS data than of data from other satellites or sensors. The number of publications (citations) of Landsat and MODIS accounts for 40.2% (45.7%) and 31.7% (39.7%) of the total and both of these have continued to increase rapidly. Landsat provides the longest global record of EO data with a medium spatial resolution [49]. Since open access to Landsat data became available in 2008, these data have supported many studies, especially in the field of land use-land cover change detection [67; 68; 69; 70]. MODIS has seven bands that have greatly improved spectral, spatial, geometric, and radiometric attributes and are explicitly designed for land applications; these data thus provide significant new opportunities for research in the field of global land use-land cover mapping and to replace the use of AVHRR data [71]. Another important reason why Landsat and MODIS data are widely used is that a large amount of analysis ready data (ARD) or standard data products are prepared such as surface reflectance (SR), top of atmosphere (TOA), quality assessment (QA) bands of Landsat, gross primary productivity (GPP), net primary productivity (NPP), and vegetation index products (NDVI and EVI) of MODIS [72; 73]. These global data are widely used to explore global change, and are being used by scientists from a variety of disciplines (e.g., oceanography, biology, and atmospheric science) [74; 75; 76]. The satellite that seems to show the most promise is Sentinel, for which the rate of increase in the number of related applications has been the fastest. Sentinel-1A was launched in 2014 and was the first in its series; a further seven satellites were launched over the next few years. However, as of 2020, the total number of Sentinel (4016) papers was still less than the total numbers of Landsat (18,366), MODIS (14,355), and AVHRR (4186) papers. For papers published in 2020, the number of Sentinel papers (1635) was still less than the number of Landsat papers (2059), but far more than the number of MODIS (1384) AVHRR papers (73). Sentinel is a series of next-generation EO missions developed by the European  
Figure 1: Number of (**a**) publications and (**b**) publications (bar) and citations (line) related to Earth observation satellites (the graphic inside is a zoom of dense area). Space Agency (ESA) and aims to replace the older EO missions to ensure a continuity of data. The Sentinel missions are focused on a range of aspects of EO (i.e., the atmosphere, the oceans, and land monitoring).