# Near-Real-Time Detection of Insect Outbreaks in Urban Trees Using a PlanetScope Time Series
## 1 Introduction
The timely identification of infested areas allows for the implementation of targeted control measures, thus helping to limit the spread of invasions and minimize the associated damage [19]. The use of satellite-based monitoring for insect infestations is a fundamental approach to large-scale natural resource management [20]. This approach, which is particularly advantageous when considering remote or hard-to-reach areas where traditional ground-based monitoring methods may be impractical, is also useful in urbanized environments, providing standardized, high time-frequency data, allowing for the analysis of vegetation health status trends. By leveraging the ability to cover extensive areas rapidly and provide up-to-date data, satellite remote sensing facilitates the early detection of infestation signals [21]. Satellite monitoring of insect infestations utilizes high-resolution imagery and multispectral or hyperspectral data to identify changes in vegetation, such as plant decline or loss of foliage cover, which can indicate the presence of infestations [22]. Images from satellites, such as Landsat or Sentinel-2, with their global coverage, are commonly used for tree monitoring [23; 24]. Relevant tools allow for the monitoring of infestation progression over time, aiding in the prediction of the spread of pests and the planning of control actions [25]. However, the spatial resolutions of Landsat and Sentinel-2 are 30 and 10 m, respectively, and their temporal frequency of at least 5 days under cloud-free conditions may be a limitation for monitoring the progression of infestations. To overcome these limitations, PlanetScope images were used in this research. Planet Labs. Inc. operates PlanetScope, a constellation of microsatellites that collects high-resolution multispectral images in the visible and near-infrared (NIR) bands [26]. PlanetScope images offer a high spatial resolution (3 m) and a very short revisit time (1 day), features that make them extremely useful for vegetation and land monitoring. To test a georeferencing and radiometric correction method, [PERSON] et al. [27] used PlanetScope imagery to identify changes in land cover. [PERSON] [28] used PlanetScope to produce a near real-time disturbance alert system that could generate a new forest change map for each released PlanetScope image. Furthermore, in the forestry sector, [PERSON] [29] combined PlanetScope and Sentinel-2 images with other information layers to map the presence of mountain pine (_Pinus mugo_ Turra) in the Sarntal Alps. PlanetScope imagery has also been used in agriculture by [PERSON] [30] to map damage to rice crops. Even in the highly urbanized context of Zagreb, Croatia, PlanetScope images have been used to map allergen species in green areas [31]. Thus, its high spatial and temporal resolution represents a significant advancement compared to Sentinel-2 (10 m spatial resolution and 5-day revisit time) and Landsat images (30 m spatial resolution and 15-day revisit time). These characteristics make PlanetScope images extremely useful for numerous applications. In this study, PlanetScope imagery was chosen, even considering the limited size of the urban areas to be monitored. The ability to work with more uniform pixels provides greater reliability. In Sentinel-2 or Landsat, the mixed pixel effect is too pronounced for this specific context [32], particularly in terms of relating remotely sensed data to georeferenced data surveyed on the ground. Remote sensing becomes more reliable when complemented by ground-based monitoring [33; 34]. Usually, data are collected during field surveys, where specialized technicians manually inspect plants and gather information on insect presence [35] and the extent of the infestation. Despite its accuracy, ground-based monitoring has several limitations. It is labor-intensive and costly, requiring specialized personnel and considerable time to cover large areas [36]. Additionally, it is challenging to obtain a comprehensive view of the situation, as access to certain areas may be limited.