Author
 |
Sadler, Edward |
|
Submitted to: Proceedings of the Conference on Biometeorology and Aerobiology
Publication Type: Proceedings Publication Acceptance Date: 1/28/1996 Publication Date: N/A Citation: N/A Interpretive Summary: Dew on leaves promotes disease, thus decreasing yield and quality. Also, dew delays field work, fall harvests, lawn mowing, and outdoor recreation. A recent paper proposed a method to detect dew using infrared thermometers, the kind of handheld gun one points at a surface to read temperature. The method basically assumes that when the leaf temperature rises above the dew point, the leaf is dry. We tested this method under the heavy dew conditions of the SE USA. We found that by making two simple changes to the method, one can improve it by about 15-20 minutes in the morning. We suspect that similar improvements could be made in the evening. The changes necessary to improve the method are easy to make and should make the method more useful in humid regions. The method as originally published could still be used in most areas without significant error. Technical Abstract: Wet conditions on leaves promote disease development, decreasing quality and quantity of harvested crops. Also, dew affects field work, fall harvests, lawn mowing, and outdoor recreation. Knowledge of wetness duration is therefore sufficiently important that innovative techniques have been developed to detect it. A recent study proposed to detect leaf wetness using infrared thermometry; when the leaf temperature rises above the dew point, the leaf has dried. This procedure worked for soybean canopies in western NE, but experience suggested it may underestimate leaf wetness duration in humid regions. Theory and data indicate that their method can be refined and thus generalized for use in more humid areas. The canopy is 1) accumulating moisture when at the dew point, 2) drying but still wet when at the wet bulb, 3) showing a partly wet, partly dry surface to the infrared thermometer while the temperature rises to a point 4) in balance with the environment and relatively steady. For light dew, the duration of the stages 2 and 3 may be very short, a few minutes or so. Experiences in the humid SE USA are that dew is both common and quite heavy. We examined if the endpoint should be delayed until leaf temperature exceeds the wet bulb rather than dew point temperature, and found from 0-20 min differences between these endpoints in a 22-d data set. The endpoint also depended on the direction the sensor faced. East- facing sensors are expected to better indicate the end of wetness. |
