ABSTRACT This work analyzes remote sensors' usefulness to analyze vegetation cover and water bodies in conservation and environmental studies. This research aims to determine satellite images' applications in coverage studies and to ascertain UAV uses (Unmanned Aerial Vehicles) in environmental studies. The determination of the applications of satellite images and the UAV was made by reviewing scientific articles, theses, books, and abstracts at conferences. A total of twenty applications were found for coverage and water body studies using satellite images and UAV. For environmental studies using satellite images, ten studies were reported. These are forest cover, urban expansion, vegetation indices, vegetation cover change, deforestation, the spatial distribution of water, water monitoring, lagoon dynamics, water quality parameters, and the Normalized Difference Snow Index thresholds. Otherwise, for environmental studies using the UAV, ten studies were reported. These are plant abundance, plant population dynamics, ecological conservation, aquatic vegetation, vegetation mapping, water quality, fluvial dynamics, river flow, bathymetric maps of a lake, and aquatic plant variations. It is concluded that the physical principles of remote perception explain through laws the operation of sensors to provide satellite information, such as satellite images that provide information with a resolution less than 10 meters, applied to studies of areas of significant extension (Km). For small areas, an Unmanned Aerial Vehicle (UAV) is used to obtain real and accurate information, which is implemented with a multispectral camera to provide information with a resolution greater than 10 cm. Therefore, it is necessary to know the limitations, advantages, and differences of these two systems to plan investigations that use this information and contribute to the protection and conservation of areas affected by natural and anthropogenic elements. | RESUMEN Este trabajo evalúa la utilidad de sensores remotos para el análisis de cobertura vegetal y cuerpos de agua en estudios de conservación y medio ambiente. La investigación tiene como objetivos determinar las aplicaciones de imágenes satelitales en estudios de cobertura y los usos de los VANT (Vehículos Aéreos No Tripulados) en estudios ambientales. La determinación de las aplicaciones de imágenes satelitales y de los VANT se realizó mediante la revisión de artículos científicos, tesis, libros y resúmenes en congresos. Se encontraron un total de veinte aplicaciones para análisis de cobertura y cuerpos de agua empleando imágenes satelitales y VANT. Para análisis ambientales mediante imágenes satelitales se reportaron diez estudios: cobertura boscosa, expansión urbana, índices de vegetación, cambio de coberturas vegetales, deforestación, distribución espacial del agua, monitoreo del agua, dinámica lagunar, parámetros de calidad de agua y los umbrales del Índice de Nieve de Diferencia Normalizada. Para análisis ambientales mediante los VANT se reportaron diez estudios: abundancia vegetal, dinámica de la población de plantas, conservación ecológica, vegetación acuática, ma-peo de vegetación, calidad del agua, dinámica fluvial, flujo de ríos, mapas batimétricos de un lago y variaciones vegetales acuáticas. Se concluye que los principios físicos de la percepción remota explican, a través de leyes, el funcionamiento de los sensores para brindar información satelital, como imágenes satelitales que brindan información con una resolución menor a 10 metros, aplicadas a estudios de áreas de mayor extensión (km). En áreas pequeñas, para obtener información real y precisa, se usa un Vehículo Aéreo No Tripulado (VANT), equipado con una cámara multiespectral que brinda información con una resolución mayor a 10 cm. Por lo tanto, es necesario conocer las limitaciones, ventajas y diferencias de estos dos sistemas, con el fin de planificar investigaciones que utilicen esta información y contribuyan a la protección y conservación de áreas afectadas por elementos naturales y antrópicos.

Observations of water surface elevation (WSE) and bathymetry of the lagoons and cenotes of the Yucatán Peninsula (YP) in southeast Mexico are of hydrogeological interest. Observations of WSE (orthometric water height above mean sea level, amsl) are required to inform hydrological models, to estimate hydraulic gradients and groundwater flow directions. Measurements of bathymetry and water depth (elevation of the water surface above the bed of the water body) improve current knowledge on how lagoons and cenotes connect through the complicated submerged cave systems and the diffuse flow in the rock matrix. A novel approach is described that uses unmanned aerial vehicles (UAVs) to monitor WSE and bathymetry of the inland water bodies on the YP. UAV-borne WSE observations were retrieved using a radar and a global navigation satellite system on-board a multi-copter platform. Water depth was measured using a tethered floating sonar controlled by the UAV. This sonar provides depth measurements also in deep and turbid water. Bathymetry (wet-bed elevation amsl) can be computed by subtracting water depth from WSE. Accuracy of the WSE measurements is better than 5–7 cm and accuracy of the water depth measurements is estimated to be ~3.8% of the actual water depth. The technology provided accurate measurements of WSE and bathymetry in both wetlands (lagoons) and cenotes. UAV-borne technology is shown to be a more flexible and lower cost alternative to manned aircrafts. UAVs allow monitoring of remote areas located in the jungle of the YP, which are difficult to access by human operators.