Sherwood B. Idso

Remote-Sensing of Crop Yields

Our research efforts with durum wheat have led to the development of the SDD concept. Its application makes possible crop yield estimates from remotely acquired canopy temperatures and auxiliary air temperature measurements obtained during the period from head emergence to the cessation of head growth. Canopy albedo measurements appear adequate to delineate this critical period, making the technique potentially adaptable to predictions of crop yields by remote-sensing. The trifactor nomograms produced from combinations of the linear regression equations also suggest that the SDD concept may be used for scheduling irrigations by remote-sensing.

The climatological significance of a doubling of earth's atmospheric carbon dioxide concentration

The mean global increase in thermal radiation received at the surface of the earth as a consequence of a doubling of the atmospheric carbon dioxide content is calculated to be 2.28 watts per square meter. Multiplying this forcing function by the atmospheres surface air temperature response function, which has recently been determined by three independent experimental analyses to have a mean global value of 0.113 K per watt per square meter, yields a value of ≤ 0.26 K for the resultant change in the mean global surface air temperature. This result is about one order of magnitude less than those obtained from most theoretical numerical models, but it is virtually identical to the result of a fourth experimental approach to the problem described by Newell and Dopplick. There thus appears to be a major discrepancy between current theory and experiment relative to the effects of carbon dioxide on climate. Until this discrepancy is resolved, we should not be too quick to limit our options in the selection of future energy alternatives.

Estimating Evaporation: A Technique Adaptable to Remote Sensing

A procedure is presented for calculating 24-hour totals of evaporation from wet and drying soils. Its application requires a knowledge of the daily solar radiation and the maximum and minimum air temperatures (standard Weather Service measurements), moist surface albedo (readily estimated or obtainable from a one-time measurement), and maximum and minimum surface temperatures (obtainable from surface or airborne sensors). Tests of the technique on a bare field of Avondale loam at Phoenix, Arizona, have shown it to be independent of season.

Net photosynthesis of sour orange trees maintained in atmospheres of ambient and elevated CO2 concentration

Eight sour orange trees planted directly into the ground at Phoenix, Arizona, as small seedlings in July 1987 have been enclosed by four clear-plastic-wall, open-top chambers since November of that year. Half of the trees have been continuously supplied with a CO2-enriched atmosphere consisting of an extra 300 cm3 of CO2 per m3 of air. Data from a comprehensive inventory of all above-ground plant parts at the conclusion of two full years of growth under these conditions have revealed that the net effect of the CO2-enriched air was to more than double the normal production of biomass over that time interval. Here we report net photosynthesis measurements made throughout the last summer of the period, which suggest that the primary impetus for this large growth response was an equivalent enhancement of the net photosynthetic rates of the CO2-enriched trees.

Compensating for Environmental Variability in the Thermal Inertia Approach to Remote Sensing of Soil Moisture

Abstract A procedure is developed for removing data scatter in the thermal inertia approach to remote sensing of soil moisture that arises from environmental variability in time and space. It entails the utilization of nearby National Weather Service air temperature measurements to normalize measured diurnal surface temperature variations to what they would have been for a day of standard diurnal air temperature variation, arbitarily assigned to be 18°C. Tests of the procedures basic premise on a bare loam soil and a crop of alfalfa indicate it to be conceptually sound. It is possible the technique could also be useful in other thermal inertia applications, such as lithographic mapping.

Planetary Radiation Balance as a Function of Atmospheric Dust: Climatological Consequences

An analysis of several atmospheric dust-loading events at Phoenix, Arizona, under background cloudless sky conditions, allowed determination of dust-induced changes in both the net solar and net thermal radiation received at the earths surface. The resultant climatological forcing function for surface temperature change was plotted against the ratio of diffuse to normal-incidence solar radiation. It was found that initial increases in atmospheric dust concentration tend to warm the planets surface. After a certain critical concentration has been reached, continued dust buildup reduces this warming effect until at a second critical dust concentration a cooling trend begins. This second critical dust concentration is so great, however, that any particulate pollution of the lower atmosphere by man will have a tendency to increase surface temperatures. Thus, anthropogenically produced tropospheric aerosols cannot be looked on as offsetting the warming tendency of increased carbon dioxide: their concurrent buildups must inexorably tend to warm the planets surface.

Effects of panicles on infrared thermometer measurements of canopy temperature in wheat

Abstract A study was conducted in Phoenix, AZ on stressed and unstressed field plots of Anza wheat ( Triticum aestivum L.) on an Avondale loam soil (a fine, loamy, mixed calcareous hyperthermic Anthropic Torrifluvent) to determine effects of panicles on the apparent canopy temperature and their consequent impact on the estimation of crop stress. The panicles were removed from a 1.5 × 4-m sample of each plot by extracting the peduncle from the upper sheath. For each treatment canopy radiative temperature measurements were made from vertical and oblique angles (30° from the horizontal), using an 8° field-of-view (FOV) infrared thermometer, at half-hour intervals from sunrise to sunset on 20, 22, and 30 April. Complementary measurements included leaf water potential and leaf diffusive resistance. Apparent canopy temperatures obtained from the oblique view of the canopy with panicles and under well-watered conditions were 2°C warmer than those of the unstressed canopy without panicles. In the stressed plot the canopy with panicles was 1°C cooler than that without panicles, but this effect was only noticed around 1200 MST. The temperature difference between viewing angles was apparently caused by different percentages of panicle area viewed by the radiometer. In the vertical view panicles contributed to 3% of the total viewed area while at the 30° oblique view panicles comprised 40% of the area. Since energy balance calculations of a non-transpiring cylinder with dimensions similar to a typical wheat panicle showed its temperature would remain very close to that of the surrounding air, canopy temperatures were adjusted for the proportion of panicles viewed assuming they were in equilibrium with air temperature. Results showed the corrected canopy temperatures of the canopy with panicles were the same as those measured in the canopy without panicles. Such a correction is necessary to avoid an overestimate of the stress level and an underestimate of differences between treatments. Crops with non-transpiring and/or well-ventilated morphological structures above the foliage will require this correction if radiative canopy temperatures are to be used in irrigation management programs or stress detection studies.

Quantifying effects of atmospheric CO2 enrichment on stomatal conductance and evapotranspiration of water hyacinth via infrared thermometry

Abstract Measurements of stomatal conductance and evaporative water loss from two tanks of water hyacinths growing at Phoenix, AZ, one under ambient conditions and one considerably enriched in atmospheric CO2, are reported. Stomatal conductances of plants in the CO2-enriched treatment were reduced to values half as great as those of plants in the ambient treatment at a mean mid-day CO2 concentration of 550 ppm, which resulted in a 22% decrease in total evaporative water loss; while in going from an ambient CO2 concentration of 310 ppm to a doubled concentration of 620 ppm there was a 27% decrease in evaporative water loss. Both of these physiological responses were well characterized by the Idso—Jackson plant water stress index. Additionally, it was found that the stomatal response to increasing atmospheric CO2 was identical to that induced by removing water from the plant roots, and that the reduction in evaporative water loss with increasing atmospheric CO2 was an inverse linear function of the plant water stress index — both of which phenomena had previously been theorized but never before experimentally verified.

Remote sensing for agricultural water management and crop yield prediction

Abstract Research we have conducted over the past several years relative to agricultural application of remote sensing is reviewed. In addition, new data are presented from recent experiments reported here for the first time. The subjects treated are soil moisture, evaporation, irrigation scheduling, and crop yield estimation. The analyses indicate that we have the technology at hand to successfully integrate remote sensing techniques into agricultural operations designed to enhance production via intelligent water management. Avenues for additional fruitful research are indicated.

On the stability of non-water-stressed baselines

Abstract Non-water-stressed baselines — plots of foliage—air temperature differential vs. air vapor pressure deficit — were obtained for seven different varieties of wheat and one variety of water hyacinth having three different characteristic leaf sizes in experiments conducted at Phoenix, Arizona. A single baseline was found to describe adequately the data for all seven wheat varieties; while three different baselines were required for the three different leaf-sized canopies of water hyacinth. The slopes of the three water hyacinth baselines were all identical; however, their intercepts differed by as much as 6° C.