Sensing Biological Environments with a Portable Radiation Thermometer David M. Gates The radiation environment in which plants and animals live is described. The coupling of the organism to the radiation field and the energy budget of the organism surface are discussed. A prototype of a portable ir radiation thermometer is described. This is an exceedingly useful instrument for the mea- surement of surface temperatures of organisms and of the thermal radiation of the environment. Field observations of plant and animal surface temperatures are reported for diverse and unusual ecological situations. The theory of measurement of surface temperatures using a radiation thermometer is discussed. Introduction Radiation is ubiquitous in the terrestrial environ- ment of that portion of the biosphere between the soil surface and the environs of space. All life requires energy and all organisms consume energy. The single most persistent and dominant form of energy flow in the aerial segment of ecosystems is radiation. The climate of a plant or animal, not immersed in water or soil, is primarily a radiation climate only modulated by wind or moisture. All surfaces of soil, rock, water, vegetation, and animals radiate energy proportional to the fourth power of the surface temperature. A person in a room or an animal in a cave is within a blackbody cavity at the temperature of the walls. A plant or animal out of doors is exposed to streams of electromagnetic radiation emitted by all surrounding surfaces of soil, rock, or vegetation, and by the at- mosphere or clouds. It is important for ecological purposes, in order to understand the interaction of organisms with their environment, to measure the surface temperatures of the environment and of the plants or animals. The evaporation of moisture from soil or from plant leaves cools the soil or leaf surface. Careful measure- ment of surface temperatures and comparison with the temperatures of dry or nontranspiring surfaces gives a direct indication of the rates of moisture loss. The surface temperature of an object, such as soil or rock, is the result of all elements of the climate acting simul- taneously. Climate is a four-dimensional space with all four variables in action at the same time. The important climate parameters are radiation, wind, air The author is with the Missouri Botanical Garden, St. Louis, Missouri 63110. Received 15 April 1968. temperature, and humidity. These are translated into temperature of a surface or the temperature of an organism through the flow of energy. An ir radiom- eter or radiation thermometer is an ideal instrument for remote sensing the surface temperatures of orga- nisms and objects. Infrared radiometry is useful in many fields including ecology, botany, zoology, forestry, agriculture, agronomy, hydrology, meteorology, clima- tology, and atmospheric sciences. Radiation Absorbed by Organisms Every organism radiates ir radiation according to the fourth power of its surface temperature T, and the emissivity of its surface . Every plant and animal is receiving an amount of infrared radiation R, emitted by the ground surface; an amount Ra emitted by the atmosphere and clouds; a quantity S directly from the sun; a quantity s of scattered skylight; and re- flected sunlight and skylight of r(S + s) from nearby surfaces of reflectivity r. All radiation quantities are expressed in cal cm- 2 min'. Each flux of radiation is time dependent and each may have a different spectral distribution of frequen- cies. Because the radiation from each source has a unique spectral quality, the mean absorptivity di of a plant or animal surface to each flux of radiation is different. The spectral quality of some sources of radiation is shown in Fig. 1, and the spectral absorp- tivity of selected plants and animals is shown in Fig. 2. The mean value of the absorptivity of a plant or animal surface will depend on the quantity of incident radi- ation xR 1 at each wavelength X, and is given by: fxaxRidX i - fARidX (1) September 1968/ Vol. 7, No. 9 / APPLIED OPTICS 1803
Transcript
Sensing Biological Environments with aPortable Radiation Thermometer
David M. Gates
The radiation environment in which plants and animals live is described. The coupling of the organismto the radiation field and the energy budget of the organism surface are discussed. A prototype of aportable ir radiation thermometer is described. This is an exceedingly useful instrument for the mea-surement of surface temperatures of organisms and of the thermal radiation of the environment. Fieldobservations of plant and animal surface temperatures are reported for diverse and unusual ecologicalsituations. The theory of measurement of surface temperatures using a radiation thermometer isdiscussed.
Introduction
Radiation is ubiquitous in the terrestrial environ-ment of that portion of the biosphere between the soilsurface and the environs of space. All life requiresenergy and all organisms consume energy. The singlemost persistent and dominant form of energy flow inthe aerial segment of ecosystems is radiation. Theclimate of a plant or animal, not immersed in water orsoil, is primarily a radiation climate only modulated bywind or moisture. All surfaces of soil, rock, water,vegetation, and animals radiate energy proportionalto the fourth power of the surface temperature. Aperson in a room or an animal in a cave is within ablackbody cavity at the temperature of the walls. Aplant or animal out of doors is exposed to streams ofelectromagnetic radiation emitted by all surroundingsurfaces of soil, rock, or vegetation, and by the at-mosphere or clouds. It is important for ecologicalpurposes, in order to understand the interaction oforganisms with their environment, to measure thesurface temperatures of the environment and of theplants or animals.
The evaporation of moisture from soil or from plantleaves cools the soil or leaf surface. Careful measure-ment of surface temperatures and comparison withthe temperatures of dry or nontranspiring surfaces givesa direct indication of the rates of moisture loss. Thesurface temperature of an object, such as soil or rock,is the result of all elements of the climate acting simul-taneously. Climate is a four-dimensional space withall four variables in action at the same time. Theimportant climate parameters are radiation, wind, air
The author is with the Missouri Botanical Garden, St. Louis,Missouri 63110.
Received 15 April 1968.
temperature, and humidity. These are translatedinto temperature of a surface or the temperature ofan organism through the flow of energy. An ir radiom-eter or radiation thermometer is an ideal instrumentfor remote sensing the surface temperatures of orga-nisms and objects. Infrared radiometry is useful inmany fields including ecology, botany, zoology, forestry,agriculture, agronomy, hydrology, meteorology, clima-tology, and atmospheric sciences.
Radiation Absorbed by Organisms
Every organism radiates ir radiation according tothe fourth power of its surface temperature T, and theemissivity of its surface . Every plant and animalis receiving an amount of infrared radiation R, emittedby the ground surface; an amount Ra emitted by theatmosphere and clouds; a quantity S directly fromthe sun; a quantity s of scattered skylight; and re-flected sunlight and skylight of r(S + s) from nearbysurfaces of reflectivity r. All radiation quantities areexpressed in cal cm- 2 min'.
Each flux of radiation is time dependent and eachmay have a different spectral distribution of frequen-cies. Because the radiation from each source has aunique spectral quality, the mean absorptivity di of aplant or animal surface to each flux of radiation isdifferent. The spectral quality of some sources ofradiation is shown in Fig. 1, and the spectral absorp-tivity of selected plants and animals is shown in Fig. 2.The mean value of the absorptivity of a plant or animalsurface will depend on the quantity of incident radi-ation xR1 at each wavelength X, and is given by:
Fig. 1. Spectral distribution of extraterrestrial sunlight, diisunlight at Earth's surface, cloud light, skylight, and of i
transmitted through a vegetation canopy.
where ia is the monochromatic absorptivity of the phor animal surface. The amount of surface areathat a plant or animal exposes to any stream of incidradiation R1 is different for each. Hence, the quantof radiation absorbed by a plant or animal havingstreams of radiation incident upon it is
nE diA is
Qab i=l (cal/cm2-min),A
where A is the total surface area of the organicHence, when there is incident on the organism, dirsunlight, skylight, reflected light, and thermal ir emitby the ground or atmosphere, the quantity absorlby the organism is
_ aiAiS + 2A2s + a3A3r(S + s) + a4A4Rtt + 5A5RA
It is of course possible that several of the as are eqand perhaps some of the Ai's equal one another, Igenerally they are different.
To know the amount of radiation absorbed by a phor animal, one must know the values of the quantilentering Eq. (3). The amounts of direct sunligskylight, and reflected radiation are measured vsolarimeters, pyrheliometers, or radiometers thatblackened thermopiles as the sensing elements coveby glass hemispherical domes. When measuringir radiation emitted by the ground, surface ormosphere radiometers may be used with thin hespherical domes of polystyrene. There is no mdifficult quantity to measure accurately than the msurement of radiation, because of the complexitiesgeometry (involving everything from point sourcesextended hemispherical sources), of spectral comp(tion, and of variations with time. Most radiatinstruments have an electrical output in millivowhich is indicated by means of a potentiomel
Therefore, most radiation instruments are only semi-ml~ D portable or the recording devices must operate with
electrical power. A completely portable battery-oper-ated ir radiometer that can measure the amount of irradiation from various sources would give much of theinformation required concerning the radiation char-acteristics of the plant or animal environment. Plantand animal surface temperatures are convenientlymeasured by means of an ir radiometer.
Energy Budgets of OrganismsA plant or animal, to remain viable over extended
periods of time, must gain as much energy as it loses.An organism exchanges energy with its environment by
0 radiation, convection, and evaporation. The energybudget of a flat plant leaf is written:
rect ,('l di(TI) - nh..da(Ta)ght Qab= eaTi + k D (T- Ta) + L ri + ra
(4)
where a- = the Stefan-Boltzmann constant, V = windnt speed, D = dimension of leaf in direction of wind, L =Ai latent heat of evaporation (580 cal gm-' at 300C),ent 3di(T,) = saturation density of water vapor at the leaftity temperature T, sda(Ta) = saturation density of theg ty air at the air temperature Ta, r.h. = relative humidity,
and r and r are the resistances of the diffusion path-way to water vapor within the stomates and the bound-ary laver of the leaf, respectively; k1 is a constantwhose values are discussed by Gates et al.1 The right-
(2) hand term in Eq. (4) is the transpiration rate of theleaf in gm cm- 2 min- converted to calories. The
sm. leaf temperature and transpiration rate adjust simul-'ect taneously to balance the terms of Eq. (4) so that theted leaf is neither warming nor cooling. It is seen thatbed to measure the leaf temperature is an important step
towards understanding the interaction of the environ-a ment with the plant. The leaf temperature is im-
portant with respect to the physiology of the leaf.(3) The photosynthetic rate, respiration rate, and growth
rate of a plant are temperature dependent and theual maximum and minimum temperatures a plant willbut
survive are important limits. The environment iscoupled to the plant by the flow of energy as expressedby the energy budget of Eq. (4).
The energy budget of the surface of an animal takesmuch the same form as Eq. (4) and is written:
M + Qab = EcyTr4 + k2 (V/D)1(T, - Ta) +
LE1 + LE2 + C, (5)
where M = the metabolic rate of the animal, T =the radiant temperature of its outer surface, k2 = aconvection coefficient (which, as a first approximation,is the same as for a cylinder with its axis at right anglesto the direction of wind flow), D = diameter of cylinder,E = moisture loss by sweating, E2 = moisture lossby breathing, and C = energy lost or gained by con-duction where the animal is resting on a substrate ata different temperature than its own surface tempera-ture. Hence, once again it is seen that the surfacetemperature of the organism plays an important rolein the energy budget of the organism. The surfacetemperature or radiant temperature of an animal willvary markedly over the surface of the animal. If theanimal is in sunshine, the sunlit portion of the surfacemay be very warm and the shaded portions may benear to air temperature. The radiant surface tem-perature of an animal, considered as an average of allparts of the surface, must cause a balance of Eq. (5)for steady state conditions. Often an animal is in atransient state and Eq. (5) can be violated for periodsof time more or less short compared with the time con-stant of the animal. But the animal cannot have anaverage temperature during its transient conditionsthat is far beyond its steady state requirements withrespect to body temperature. The body temperatureof an animal is related to its radiant surface tempera-ture by the conductance of its fatty tissue and of its
fur or feathers. It is not the intention to discuss thesematters in detail here. The surface of an organismconnects the internal heat transfer processes with theexternal energy from the environment and is for thisreason an extremely important quantity to know.The body temperature of many animals must remainwithin very narrow limits and this in turn puts limitson the radiant surface temperature. It turns out,however, that most animals allow for great changes inradiant surface temperature by adjusting their meta-bolic rate or their sweating rate. Some animals canvary the conductivity of their fatty tissue by changingthe venous flow or of their fur or feathers by changingthe compactness of the fur or feathers. Very little isknown about the surface temperatures of animals.
Infrared Radiometry
To understand the interaction of organisms andenvironment, it is important to known the temperatureof a plant leaf (essentially the surface temperature forthin leaves) and the radiant surface temperature of allanimals under various environmental conditions. Theideal way to measure the surface temperatures of aplant or animal is by use of an ir radiometer. In orderto obtain an estimate of the radiation absorbed by aplant or animal, it is necessary to know approximatelythe amount of ir radiation emitted by the ground sur-face and the atmosphere, which in effect requires know-ing the mean surface temperature of the ground andthe radiant temperature of the atmosphere. An irradiometer is clearly the instrument to be used to mea-sure the ir fluxes from various surfaces and to give theapparent radiant or blackbody temperature of the sur-face. An animal on the surface of the ground or plantleaves near the ground surface receives radiation fromvery specific nearby surfaces of soil, rock, vegetation,etc. An ir radiometer with a field of view of severaldegrees is the only practical way to measure thesesurface temperatures and the fluxes of radiation fromthem. The radiant temperatures and radiation fluxesof an environment can be ascertained using an irradiometer. A portable ir radiometer is necessary ifmeasurements are to be made at any field location.
Infrared radiometers of various designs have beenavailable for some time and were described by Gates.2
The radiometers available in the past generally werenonportable in that they required 110 V ac power.Stoll and Hardy3 and Stoll4 described a radiometerthat was basically portable, but limited for some typesof field use. Gates5 reported many results using theStoll-Hardy radiometer which, although intended anddesigned primarily for laboratory measurements, couldbe used in the field when certain precautions weretaken. The Stoll-Hardy radiometer is a dc or non-chopped radiation instrument and is subject to driftas a result of temperature change of the instrument.Care with its use, including heavy insulation of thesensing unit, reduced measurement errors to a mini-mum. The problem of thermal drift in a radiometeris reduced when the input signal is chopped against acomparison signal from a built-in blackbody radiator.
Fig. 4. Prototype model of the portable ir radiometer PRT-10showing the temperature dial.
Fig. 5. Optical diagram of the portable ir radiometer.
Portable Infrared Radiometer
The portable ir radiometer, model PRT-10, de-signed by the staff of Barnes Engineering Company,is a self-contained instrument for taking surface tem-perature measurements without making contact withthe target surface. A prototype model of the battery op-erated radiometer is shown in Figs. 3 and 4. It operatesfor approximately 100 h without requiring a change ofbatteries. The radiometer, shown in cross section inFig. 5, has no moving parts and uses a blackened evap-orated thermopile ir detector. An electronic choppercompares the incoming signal with the temperature ofthe cold junctions of the thermopile, which are at theambient temperature of the instrument. A blockdiagram is shown in Fig. 6. The radiometer is wellinsulated and yet is compactly designed in the form ofa gun that is easily hand held.
A polyethylene window seals the entrance apertureand spectral filters limit the passband to the 8- 20-wavelength region. Ostensibly, sunlight is eliminatedfrom the instrument, but temperatures of sunlit sur-faces should not be measured with the instrument
pointed in the direction of specular reflection to thesun.
Measurements are made easily by pointing the radi-ometer at the target of interest and reading the tem-perature directly from the meter on the rear of theinstrument. The instrument is designed primarilyfor use with targets at close range. Its field of view is1.27 cm in diameter at a nominal working distance of1.27 cm. For examining distant objects, the field ofview is approximately 35° wide. The prototype modelhas two modes of operation: (1) an absolute temper-ature range of - 10C to +60'C and (2) a differentialtemperature range of 50 C about any selectable mid-scale temperature for detailed thermal analyses. Thetemperature sensitivity is 0.1C and response time is0.75 sec. The instrument weighs approximately 1 kg.
Theory of Measurement
Fuchs and Tanner' have discussed the theory of re-mote sensing of surface temperatures using radiometersand pointed out the error that can result when theemissivity of the surface is less than 1.0. A radiationthermometer will not sense the true surface tempera-ture of an object if the reflectivity of the surface issuch that it reflects a radiation flux that is substan-tially different from the radiation emitted by the sur-face. If the surface has a reflectivity of any value andthe surface is imaging other sources of radiation suchas the sun or a very cold sky, the radiometer may notread the true surface temperature. In the case of thereflected sunlight, the instrument will indicate too higha surface temperature. In the case of a cold sky,the radiometer will indicate too low a surface tempera-ture, providing the actual surface temperature of theobject is substantially warmer than the radiant tem-perature of the sky. If the surface whose temperatureis being sensed radiometrically is surrounded by othersources of radiation that are more or less at the sametemperature, there is little error in the measured valueof the surface temperature.
The theory of radiometric determination of surfacetemperatures developed by Fuchs and Tanner is partly
reproduced here for the convenience of these readers.A monochromatic flux of radiation B(X,T8 ) is incidentto the surface from the environment that has an in-tegrated radiative temperature T The surface hasa monochromatic emissivity Ex, hence a monochromaticabsorptivity equal to Ex, and a monochromatic re-flectivity (1 - Ex). The blackbody radiation emittedby a surface at temperature T is E(X, T) as described byPlanck's radiation law. The total outward flux ofmonochromatic radiation from the surface in a smallwavelength interval between X and ( + dX) is
W(X)dx = exE(XT)dx + (1 - ex)B(X, T8)dX. (6)
The radiometer senses some fraction f(X) of the outwardflux of radiation according to the instrument response,where 0 < f(X) < 1 and responds to an apparent fluxRo(X), which is given by:
Ro(x)dX = f(X)W(X)dX. (7)
The total apparent outward flux of radiation mea-sured by the radiometer
fco0 exf(X)E(X, T)dX + (1 - ex)f(X)B(X, T,)dX.
0 fo,~J(8)
The emissivity of the surface weighted for the in-strument response is defined by:
= [ Ef(x)E(X, T)dx7 [f f(X)E(X, T)dx] (9)
In the ambient temperature range for the surfacesof organisms and terrestrial temperatures, e is verynearly independent of temperature.
It is also convenient to define a mean filter functionf(T) as:
f(T) = f (x)E(, T)dx] [ E(X T)dX]. (10)
Since
E(X, T)dX = o-T4 ,
then
f f(X)E(X, T)dX = f(T)T 4. (12)
The filter characteristics for the Barnes ir radiometerare described approximately as follows:
The spectral form or distribution of B(X, T,) is oftencomplex since it may be a mixture of radiation fluxesfrom several sources. In fact, its precise form may beunknown for many situations. The last term in Eq.(8) is integrated easily only if one assumes constantemissivity in the significant portion of the spectrum.Hence, if cx = e, then Eq. (8) becomes
Ro = ef(T)a-T4 + (1 - e)f(T)Ba. (17)
This is the fundamental equation describing thequantity of radiation received at the detector of theradiometer. Since the absolute value of f(T) is notimportant, but only its form, an assumption is nowmade that f(T) is constant for the range of environ-mental and organismal temperatures encountered.The radiometer is calibrated according to a quantityRb Ro/f(T). Hence,
Rb = ea-T4 + (1 - e)Bs* = Ta4 ,
where Ta is the apparent surface temperature and
B,* = [f(T8)/f(T)1B0 .
(18)
(19)
The quantity B,* has little physical meaning since itis related to the general flux B of radiation incidenton the surface whose temperature is being observed.The radiometer interprets the true surface temperatureT to be the apparent surface temperature Ta. If e =1, then Ta = T. Also, if the radiative temperatureof the surroundings is equal to the real surface tem-perature, then Ta = T. If the surface has an emissiv-ity substantially less than unity and if the surfaceimages the sun or a cold sky, the apparent surfacetemperature as measured with the ir radiometer maybe quite different from the true temperature. For-tunately, nearly all biological materials, plant and ani-mal surfaces, are nearly black7 and have emissivitiesbetween about 0.95 and 0.98.
The user of any ir radiometer should take the pre-caution of calibrating his own instrument. This isdone simply by means of a Leslie cube which contains ablackened reentrant cone at the temperature of thecube.
Field Observations
The ir radiometer described in this paper was usedduring the summer of 1967 under extreme conditionsof cold wind of the alpine tundra of the Rocky Moun-tains of Colorado; of the hot, semiarid conditions ofwestern Colorado and eastern Utah during July andAugust; and in the midwest during autumn andwinter. It was used in Australia and New Zealandduring January and February 1968, which is the
Fig. 7. Temperatures of plants are according to the position ofthe appropriate symbol.
southern hemisphere summer. The radiometer isextremely useful in the laboratory, in greenhouses,and to measure the radiation climate within growthchambers. Plant temperatures were measured at alltimes of day in many places. The surface tempera-tures of numerous animals were measured, includingyoung birds in a nest, pika, garter snake, many varietiesof lizard, hedgehog, deer, koala bear, wallabys, wombats,humans, dogs, and insects, including many orthoptera,coleoptera, bumble bee, grasshoppers, and larvae suchas caterpillars. At all times and places, the environ-mental temperatures were measured, including soil androck surface, nearby vegetation, sky, clouds, and otherobjects.
An opportunity occurred to measure the tempera-ture of deer antlers in velvet and to show that the radi-ation from the antlers represents an important lossof heat in terms of the total energy budget for the ani-mal. The measurement was made with a tame reddeer in New Zealand. The air temperature was 15'C,the body surface temperature was 17'C, the surfacetemperature of the head was 250 C, and of the antlers,28'C. The sky was overcast with clouds at a radianttemperature of 10'C and the grass covered groundsurface was at 15'C. There was no wind. An evalu-ation of the total radiation loss from the animal showsthat the antlers radiate about 20% of the total. Re-cently, this same type of observation was repeated withthe measurement of the temperature of a new antleron a female reindeer in a shed at the St. Louis Zoo.The antler was at 320C when the air and wall tempera-tures of the shed were at 150C and the body surfacetemperature was 17'C.
The energy budget for a plant leaf, as expressed byEq. (4), shows that there are three primary mechanismsby which a plant leaf may prevent its temperaturefrom rising too high above air temperature. First, aleaf may, by various means, keep the amount of radi-ation absorbed by it to a low value. The leaf maydo this by having a low absorptance to the incidentradiation (by having a high reflectance and/or a hightransmittance). A leaf may reduce the amount ofradiation absorbed by presenting a relatively small
area to the flux of incident radiation, such as orient-ing with an edge towards the sun or by having a cylindri-cal shape, such as a needle. Second, a leaf may trans-pire freely and thereby keep its temperature reducedby evaporative cooling. Third, a plant may haveleaves of small dimension and remain near to air tem-perature by convection. Some leaves use all threemechanisms simultaneously, some two or one and someuse none of them. Whether the leaves of a givenspecies actually find it necessary to remain cool isdifficult to say, but there are many pieces of evidenceto suggest that plant leaves may get too warm to re-main physiologically active, or indeed viable.
The most striking control of leaf temperature ob-served was with Erythrina indica, near Sydney, Aus-tralia at noon, whose leaves were approximately 8 cm X10 cm and were pointing nearly vertical. With anair temperature of 320C, sky at a radiant temperatureof 16'C with high cirrus, bright sun and no wind, thevertical sunlit leaves were at 36-38oC. The shadeleaves, which were receiving reflected radiation fromthe ground and emitted longwave radiation from theground and nearby objects, were at 330 C. Some ofthe leaves of Erythrina indica, which were horizontaland receiving the sun nearly normal to their surface,were at 42-44°C. A few meters away was a tree ofPopulus deltoides, whose leaves were about the samesize as the Erythrina leaves, were primarily horizontaland fully exposed to the direct sunlight, were at 32-34°C with the air temperature 320C. Shade leavesof Populus deltoides were at 300C. It is evident fromenergy budget considerations that Populus deltoideswas transpiring much more than Erythrina. A jaca-randa tree, Jacaranda acutifolia, with small leaves ex-posed to full sun had leaf temperatures not exceeding
701
6o
50
* 40a
30
20
10
0
Neo Above2Abago Pss eflh hieCanyos1 IL IL Z
Ele 9200' i 7 to Reef |oalder90 J 29 July Notlonal Coyan,
i/A S~~~~~~older C.p3 M.onumrT Colorodo
S Ag 30 July 21 July
LiP S W 5J-¢G FYR
0 R FiY
LuS
- oa 0 Dondelion= A Aspen
G GrassesS Soge bush0 Gamble's Ok V Verbascum
\ _ H Sufltowr R RibesD AO W Sookewed Lu Lucerne
J Juniper F FirG - P Pinyon Pine Y Ponderosa Pine
Ag AgoveSoil surfac temperature
D0° Arl tempertre -
0600 1000 1400 100 1000 1400 1700TIME OF DAY
Fig. S. Temperatures of plants at various sites and times ofday as measured with the portable ir radiometer.
air temperature by 30 C. The leaves of jacaranda werecooled by convection because of their small size. Thissame phenomenon was reported by Gates et al.' for thenumerous small leaved plants of semiarid regions inUtah and Colorado. The influence on leaf temperatureof strong convective cooling was confirmed by calcula-tion based on Eq. (5).
The portable ir radiometer was used to measure en-vironmental, plant, and animal temperatures during afield trip to Colorado and Utah in July and August,1967. The results of some of these measurements areshown in Figs. 7 and S. It is evident that only thelarger succulent plants such as Agave and the cactusOpuntia had temperatures substantially above airtemperature. The surface temperatures of lizardswere measured by tethering them and letting themmove freely to select a position in sun or shade. Lizardsurface temperatures were more closely aligned withthe substrate surface temperature of the soil ratherthan with the air temperature. This is as one wouldexpect for a poikilotherm at the ground surface.
The portable ir radiometer indicated the radianttemperatures of clear skies to be less than -10'C andof overcast skies between - 50 C and 10'C in variouslocalities. Radiant sky temperatures as low as - 750Chave been reported 8 and are often -20 or -30°C fordry, clear air. Surface soil temperatures may reach70'C when direct sunlight incident on the surface is
very intense. Many microorganisms live in soils andlichens grow on the surfaces of rocks where tempera-tures may exceed 600C in full sunlight.
The author wishes to thank Warren Porter, RonaldAlderfer, and Elwynn Taylor for assisting with someof the field measurements and Laverne Papian for thecomputer programming of the energy budget equations.The author is grateful to the staff of the Barnes Engi-neering Company for their persistent efforts to designa convenient, reliable, and versatile ir radiometer forfield use, which will contribute significantly to ourunderstanding of radiation environments and theenergy budgets of plants and animals.
This work was supported by a grant to the MissouriBotanical Garden from the U. S. Atomic Energy Com-mission and by the Center for the Biology of NaturalSystems, Washington University, under a PHS grant.
References1. D. M. Gates, R. Alderfer, and E. Taylor, Science 159, 994
(1968).2. D. M. Gates, Energy Exchange in the Biosphere (Harper and
Row, Inc., New York, 1962).3. A. M. Stoll and J. D. Hardy, J. Appl. Physiol. 5, 117 (1952).4. A. M. Stoll, Rev. Sci. Instrum. 25, 184 (1954).5. D. M. Gates, Science 134, 32 (1961).6. M. Fuchs and C. B. Tanner, Agron. J. 58, 597 (1966).7. D. M. Gates and W. Tantraporn, Science 115, 613 (1952).8. J. D. Hardy and A. M. Stoll, J. Appl. Physiol. 7, 200 (1954).
Love Song from a Hollow Cathode
LINES WRITTEN AFTER SEEING WARREN KREYE'SSPECTROSCOPY EXPERIMENT TO MEASURE THE
DOPPLER PROFILE OF THE SPECTRUM OF GOLD FROMAN ARGON-FILLED GOLD HOLLOW CATHODE.
Ares' fleece is too solid sullied stuff forLove the golden light has an airyFunction we cannot do without.If this present argonaut would seekTo know the warmth of golden thrustIn hollowness and thus to find the peak,Some alchemy must breathe through his air,A colorless odorless elementThat penetrates but will not bind-Argon makes such golden atmosphere.So breathe you argon on these my golden wallsAnd gold to airy thiness beat.
The poem has literary as well as spectroscopic allusions: the Golden Fleece sought byJason and the Argonauts hung in the temple of Ares, the Greek god of war and strife.The first line is an experimental application of a theoretical debate on Shakespeare's spell-ing. Critics cannot decide whether Hamlet said: " that this too too solid flesh wouldmelt/Thaw and resolve itself into a dew" or "too too sullied. . ." Either is possible andboth are meaningful. The last line echoes John Donne, from A Valediction ForbiddingMourning:
Our two souls therefore, which are one,Though I must go, endure not yet
A breach but an expansionLike gold to airy thinness beat.
Author Mary Hynes, Department of English Submitted by Gordon Berry, Department of PhysicsUniversity of Wisconsin
Information about future meetings should be sent toP. R. WAKELING, Editorial Consultant, WINC, 1500Massachusetts Avenue, N. W., Washington, D. C. 20005
Symposium on Mechanical and Thermal Prop-erties, of Ceramics, Gaithersburg, 1-2 April 1968Reported by the NBS Office of Technical Information
Jointly sponsored by the American Ceramic Society, the Ameri-can Society for Testing and Materials and the National Bureau ofStandards, the conference-some 200 strong-concentrated onthe property-character relationship-the dependence of ceramicproperties upon microstructure and composition. Generalchairman for the conference was J. B. Wachtman, Jr., NBS.
Ceramists often make use of the thermal and mechanical prop-erties of a ceramic in the design of a part. In many cases, theseproperties influence the design of the device in which the partis to be used. The Symposium was intended to provide a basisfor understanding the property-character relationship, as well ascriteria for proper selection and use of ceramic materials.
The conference opened with a survey of the activities of ACMand ASTM, two of the principal institutions through whichAmerican ceramicists communicate and formulate standards.The presidents of ACM and ASTM, J. S. Owens and F. J.Mardulier, respectively, summarized their organizations' activi-ties in ceramics; J. C. Richmond NBS also spoke on ASTM'swork in this field.
Owens explained that an understanding of the property-character relationship and the process of character developmentduring processing are needed as a guide in producing new ce-ramics. Standard test methods for both character determinationand property measurement are therefore important aids in de-veloping this understanding. In this regard, the process bywhich U. S. standards are developed and the role of ACM andASTM in developing such standards was described.
Merely understanding the property-character relationshipand having standard test methods will not ensure the commercialdevelopment of new ceramics. This development will occuronly if justified by demand. In view of this fact, C. S. BerschBureau of Naval Weapons discussed new markets open to ce-ramics; he also emphasized the requirement for reliability with theconsequent need for good testing procedures.
The discussion of thermal properties of ceramics began with apaper on the melting points of these refractory materials by S. J.Schneider NBS. One of the factors limiting the use of ceramicsat high temperature is the development of stress accompanyingthermal gradients. Thermal shock parameters involving elasticmoduli and thermal expansion have been used as a rough guideto the thermal shock resistance of materials, but it has long beenrecognized that a complete analysis of the heat flow and tempera-ture distribution for each particular device is needed. Theproperties needed for such analysis were covered by R. K.Kirby (thermal expansion), D. R. Flynn (thermal conductivity),and J. C. Richmond (thermal radiation), all of NBS.
On the second day of the symposium, the mechanical proper-ties, which determine response to stress, whether of thermal ormechanical origin, were discussed. These included presentationson elastic deformation by J. B. Wachtman, Jr., NBS, inelasticdeformation by R. M. Spriggs Lehigh University, inelastic de-formation of nonoxide ceramics by G. E. Hollox RIAS, and vis-coelasticity of glass by P. B. de Macedo Catholic University ofAmerica.
Fracture of polycrystalline ceramics resulting from stress
usually occurs suddenly and completely. Therefore, it isnecessary not only to understand the characteristics of brittlefracture, but also to design for the use of ceramics with this inmind. S. M. Wiederhorn NBS approached the subject from twopoints of view: fracture mechanics as a branch of continuummechanics and effects of defects and environment. Finally,the subject of mechnical testing was treated in a separate paperby L. Mordfin and M. J. Kerper Office of Aerospace Research.
The Proceedings of this Symposium will be published by NBSand should be available by January 1969.
MRI Symposium on Turbulence of Fluids andPlasmas, New York City, 16-18 April 1968Reported by Victor Twersky, University of Illinois at Chicago
When you know you are going to talk on a special topic withinthe format of a relatively unfamiliar broad discipline, you makesome effort to learn about the other subject. In addition, whena major journal wants the meeting covered (and you put theletter aside while you try to think of someone more appropriate,and stumble across it too late to slough it off), you make an addi-tional effort. You read about the subject before the meeting andpay close attention during the talks, but a month later when yousit down to write, all you remember is the opening session ofbroad survey papers (or at least some of the jokes), the sessionin which you participated, and the cocktail party. However, ifyou were lucky enough not to lose the program of abstracts, youcan still try to make a go of it.
The four to five hundred attendees at the Waldorf-Astoriafor the Symposium on Turbulence of Fluids and Plasmas (theeighteenth in the PIB series in electrophysics) were welcomedby E. Weber (President, Polytechnic Institute of Brooklyn),C. D. Y. Ostrom, Jr. (Director, Army Research), I. C. Atkinson(Commander, Air Force Office of Scientific Research), E. H.Weinberg (Director, Physical Sciences, Office of Naval Research),H. R. Mimno (Director, Region I, Institute of Electrical andElectronics Engineers), and by A. F. Turner (President, OpticalSociety of America). All the sponsoring organizations are citedwithin these parentheses; M. H. Bloom and R. G. E. Hutter(the co-chairmen of the MAlicrowave Research Institute Com-mittee that arranged the symposium) should also be mentioned.
A remarkable feature of the informative and excellent openingsession-Introduction to Turbulence-was the ordering of topics.It began with the summary by F. N. Frenkiel Navy Ship Re-search and Developnient Center (who also chaired the session),continued with T. H. Dupree's survey of the additional basicphenomena associated with turbulence in plasmas, and endedwith L. S. G. Kovasznay's elegant tutorial introduction to tur-bulence in simple fluids.
Reversing the original ordering, Kovasznay Johns Hopkinsbegan with three criteria for turbulence in fluids: randomness atthe microscopic level (an absence of long range order, so that nopermanent oscillations develop), three-dimensionality (so that"vortices stretch" instead of being preserved as in two dimen-sions), and nonlinearity (for energy conversion from the originalstreamline flow). He described and illustrated the principalroutes by which fluids in steady laminar flow could become tur-bulent-from the build-up of small linear instabilities, on to largedisturbances corresponding to different localized transition re-gions. However, he also pointed out that the small disturbancesmight lead to amplitude limited periodic flow and that the largedisturbances might decay and cause the flow to again becomelaminar. He discussed five forms of fully developed turbulence:first a set of three that did not involve boundaries and then theremaining two forms-turbulence caused by flow through grids,
