Landsat images have a relatively high spatial resolution (60 m for Landsat 1, 2, and 3 30 m for Landsat 4, 5, and 7) enabling land cover and land use characterization at the local scale. However, the low spatial resolution of these sensors (250 m for MODIS, 1 km for AVHRR) severely limits the capability of measuring individual crop field properties. Sensor systems such as the Advanced Very High Resolution Radiometer (AVHRR) and Moderate Resolution Imaging Spectroradiometer (MODIS) instruments are commonly used to study land cover phenology because of their daily repeat coverage. There are many satellite sensor systems that collect earth surface measurements at varying spatial resolutions and temporal frequencies which can be used to determine land cover conditions. However, land cover data at the frequency and resolution necessary for exposure assessment are often not available during the critical pre-diagnosis exposure periods of most epidemiological studies (e.g., date of conception until date of diagnosis in birth outcome studies). Land use and land cover maps (e.g., urban, crop type), such as provided by the California Department of Water Resources (CDWR), have been used in geographic-based transport and fate models to derive estimates of human exposure. The condition of the land cover (e.g., bare soil, vegetation) at the time of chemical application has been shown to have a significant effect on chemical drift. Determining the transport and fate of pesticide chemicals is a complex process which depends on many factors such as weather conditions, vegetation characteristics, soil properties, application method, and chemical persistence. Methods for estimating pesticide exposure are needed since environmental samples of pesticide levels in the home can only be collected after enrollment into a study (i.e., after date of diagnosis). Increased detection and/or concentration of pesticides used on crop fields adjacent to residences in biological samples of residents and house dust have been shown in several studies. We suggest additional research to determine the feasibility of integrating CDWR land use maps and Landsat data to derive crop maps in locations and time periods where maps are not available, which will allow for substantial improvements to chemical exposure estimation.Ī primary emphasis of our research is to examine the relationship between pesticides used on crops grown near individual residences and health outcomes in California.
![colt advanced media center remote mapper colt advanced media center remote mapper](https://images-na.ssl-images-amazon.com/images/I/51+1rTnbxbL.png)
Landsat data will be limited during the winter months due to cloud cover, and for years prior to the Landsat 7 launch (1999) when only one satellite was operational at any given time. The Landsat image time-series was useful for identifying idle, single-, and multi-cropped fields. We found the combination of Landsat 5 and 7 image data would clearly benefit pesticide exposure assessment in this region by 1) providing information on crop field conditions at or near the time when pesticides are applied, and 2) providing information for validating the CDWR map. Many samples designated as single-cropped in the CDWR map had phenological patterns that represented multi-cropped or non-cropped fields, indicating they may have been misclassified.
![colt advanced media center remote mapper colt advanced media center remote mapper](https://cdn.dvidshub.net/media/thumbs/frames/video/1604/457548/1000w_q75.jpg)
However, images were limited during the winter months due to cloud cover. We found the frequent overpass of Landsat enabled detection of crop field conditions (e.g., bare soil, vegetated) over most of the year. We intersected the Landsat time series with the California Department of Water Resources (CDWR) land use map and selected field samples to define the phenological characteristics of 17 major crop types or crop groups. We collected a dense time series of 24 Landsat 5 and 7 images spanning the year 2000 for an agricultural region in Fresno County. The purpose of this study was to examine the potential for using Landsat satellite data to support pesticide exposure assessment in California.
![colt advanced media center remote mapper colt advanced media center remote mapper](https://gunxperts.com/wp-content/uploads/2021/02/Combo-MS-REP-AR-BT-QD-EP-T_0-370x370.png)
![colt advanced media center remote mapper colt advanced media center remote mapper](https://virtualdj.com/image/79485/200338/firstpage_online.png)
Geological Survey policy offering Landsat satellite data at no cost provides researchers new opportunities to explore relationships between environment and health.