COLOUR AND FALSE-COLOUR AERIAL PHOTOGRAPHY ......used aerial colour photography in1959 and Sims and...

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96 PROCEEDINGS OF THE NEW ZEALAND ECOLOGICAL SOCIETY, VOl.. 17. 1970 COLOUR AND FALSE-COLOUR AERIAL PHOTOGRAPHY FOR MAPPING BUSH FIRES AND FOREST VEGETATION G. ROSS COCHRANE Departmeal of Geography. Universilyof Auckland SUMMARY: Bushfircs are common in Australia. They cau:oe much damage and considerable loss annually. However. some use could be made of these wildfires fer forest mapping if developments in colour and false-colour (colour infrared) aerial photography were more fully exploited. The advantages that colour and false-colour aerial photography have over pan~ chromatic minus-blue aerial photography are analyzed for the Australian forest '~nvironment. A technique is described. using colour or colour infrared aeri~.I film. either separately or together for multispectral analysIs. that could improve the accurate mapping of Australian sclerophyll Eucalyptus fe.rests (after fire) and provide valuable information on the effect of fire on forest ecology. This technique involves sequential aerial photography to record the "Very distinctive regeneration patterns that follow bushfires. This technique should have wide applica. tion for forest studies and for much forest mapping. both within and beyond Australia. INTRODUCTION Periodic wildfires (bushfires) have long been part of the natural environment of the sclerophyll forests of Australia. Their frequency has increased greatly over recent decades in south-western. south-eastern and eastern Australia. Accepling the inevitability of bushfires and recognising that great gaps are still presenl in detailed systemalic forest mapping within Australia. current systematic mapping could be augmented from aerial photo- graphic studies of bushfire areas. At present, inadequate use is being made of advances in aerial photography. Bushfires, instead of being regarded primarily as state or national disasters, could be used for greatly improving knowledge of distributions of sclerophyll forest trees by using colour and false- colour aerial photography, This information is urgently needed if better fire prevenlion, fire con- trol and prescribed burning practices are to be adopled (Hodgson 1967). The use of colour film would yield much more information than can be interpreted from the traditional panchromatic minus-blue (black-and-white) film currently used. The Forest Research Institute at Canberra first used aerial colour photography in 1959 and Sims and Benson (1966) have demonstrated the value of the negative-positive system of aerial colour photography for photo-interpretation of unburnt forest in Australia. False-colour or colour infrared photography (also called Infrared Ektachrome, Ektachrome l..frared Aero and Ekta Aero Infrared), which combines the visible (400 to 700 nanometre) and near infrared (700 to 950 nanometre) regions of the electromagnetic spectrum. is more useful than panchromatic, black-and-white near infrared or colour photography for mapping and identifying many plant communities. Striking contrasts between burned and living vegetation suggest that false-colour film, such as Ekla Aero Infrared, may prove much Ihe most suitable film for mapping bushfire areas. Despite Benson and Sims' (1967) condemnation Ihal "false colour film has proved of no practical advantage in the detection of inseci or disease alfected forests in Australia", they reluctantly concede "that fire etfects on snow gum (Eacalyptus niphophilia) 12 months prior to photography were more readily seen on infrared than on Ektachrome". (Sims and Benson 1960. p. 46). These authors noted that dramalic colour differences in infrared film belween healthy and fire-damaged snow gum trees appeared as similar tones on Ektachrome. and that recovery from fire, detectable in infrared cannot be detected on Ektachrome. Although the cost of positive reproduction of colour film is four times that of panchromatic film. the cost of an aerial survey in colour to the stage of a processed negative is little more than that of a black and white panchromatic coverage. The increase in costs using colour or false-colour film would be more than offset by the greater ease of inlerprelation and the additional information so oblained. The use of colour or false-colour films ralher than panchromatic film would be feasible even within the tight budgetary restric-

Transcript of COLOUR AND FALSE-COLOUR AERIAL PHOTOGRAPHY ......used aerial colour photography in1959 and Sims and...

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96 PROCEEDINGS OF THE NEW ZEALAND ECOLOGICAL SOCIETY, VOl.. 17. 1970

COLOUR AND FALSE-COLOUR AERIAL PHOTOGRAPHY

FOR MAPPING BUSH FIRES AND FOREST VEGETATION

G. ROSS COCHRANE

Departmeal of Geography. Universilyof Auckland

SUMMARY: Bushfircs are common in Australia. They cau:oemuch damage and considerableloss annually. However. some use could be made of these wildfires fer forest mapping ifdevelopments in colour and false-colour (colour infrared) aerial photography were more fullyexploited. The advantages that colour and false-colour aerial photography have over pan~chromatic minus-blue aerial photography are analyzed for the Australian forest '~nvironment.A technique is described. using colour or colour infrared aeri~.I film. either separately or

together for multispectral analysIs. that could improve the accurate mapping of Australiansclerophyll Eucalyptus fe.rests (after fire) and provide valuable information on the effect offire on forest ecology. This technique involves sequential aerial photography to record the "Verydistinctive regeneration patterns that follow bushfires. This technique should have wide applica.tion for forest studies and for much forest mapping. both within and beyond Australia.

INTRODUCTION

Periodic wildfires (bushfires) have long beenpart of the natural environment of the sclerophyllforests of Australia. Their frequency has increasedgreatly over recent decades in south-western.south-eastern and eastern Australia. Accepling theinevitability of bushfires and recognising that greatgaps are still presenl in detailed systemalic forestmapping within Australia. current systematicmapping could be augmented from aerial photo-graphic studies of bushfire areas. At present,inadequate use is being made of advances in aerialphotography.

Bushfires, instead of being regarded primarilyas state or national disasters, could be used forgreatly improving knowledge of distributions ofsclerophyll forest trees by using colour and false-colour aerial photography, This information isurgently needed if better fire prevenlion, fire con-trol and prescribed burning practices are to beadopled (Hodgson 1967). The use of colour filmwould yield much more information than can beinterpreted from the traditional panchromaticminus-blue (black-and-white) film currently used.The Forest Research Institute at Canberra firstused aerial colour photography in 1959 and Simsand Benson (1966) have demonstrated the valueof the negative-positive system of aerial colourphotography for photo-interpretation of unburntforest in Australia.

False-colour or colour infrared photography(also called Infrared Ektachrome, Ektachromel..frared Aero and Ekta Aero Infrared), which

combines the visible (400 to 700 nanometre) andnear infrared (700 to 950 nanometre) regions ofthe electromagnetic spectrum. is more useful thanpanchromatic, black-and-white near infrared orcolour photography for mapping and identifyingmany plant communities. Striking contrastsbetween burned and living vegetation suggest thatfalse-colour film, such as Ekla Aero Infrared, mayprove much Ihe most suitable film for mappingbushfire areas. Despite Benson and Sims' (1967)condemnation Ihal "false colour film has provedof no practical advantage in the detection of insecior disease alfected forests in Australia", theyreluctantly concede "that fire etfects on snowgum (Eacalyptus niphophilia) 12 months priorto photography were more readily seen on infraredthan on Ektachrome". (Sims and Benson 1960.

p. 46). These authors noted that dramalic colourdifferences in infrared film belween healthy andfire-damaged snow gum trees appeared as similartones on Ektachrome. and that recovery fromfire, detectable in infrared cannot be detected onEktachrome.

Although the cost of positive reproduction ofcolour film is four times that of panchromaticfilm. the cost of an aerial survey in colour to thestage of a processed negative is little more thanthat of a black and white panchromatic coverage.The increase in costs using colour or false-colourfilm would be more than offset by the greater easeof inlerprelation and the additional informationso oblained. The use of colour or false-colourfilms ralher than panchromatic film would befeasible even within the tight budgetary restric-

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tions that may apply in Australia. Aerial colourphotography was used in Tasmania following the1967 bushfires about Hobart.

Although in no way belittling the contributionsmade by systematic mapping by Forestry depart-ments within available map units and State forestsor the use of aerial colour photography over thelast four years by the Australian Forest ResearchSchool, much Australian forest remains virtuallyunmapped and little is known of the ecology ofmany areas. In bushfire areas the use of sequentialaerial coJour or aerial false-colour photography,or both - even in forests of very mixed speciesor mixed age stands - could substantially aug-ment knowledge of forest species' distribution andcomposition. I am fully aware that fire intensity,which varies with a multitude of factors includingseason, slopes, aspect, fuel accumulation, wind.fire history, age and composition of forests, affectsregeneration patterns (Cochrane 1963, 1966,1968a, I 968c, 1969, Cochrane et al. 1968). How-ever, detailed ecological studies of a complexburned area for four years after a fire indicate thatdistinctive patterns of species regeneration areoften more dominant than variations resultingfrom differences in fire intensity. Evidence to date,therefore, is sufficiently encouraging to warrant athorough testing programme of the use of bothcolour and false-colour aerial photoraphy for: (a)accuratelv delimiting burned from unburnedareas, (b) mapping the distribution of differentEucalvptus associations following bushfires. (c)planning catchment control. firebreak construc-tion and maintenance, Jogging. controlled burningand silvicultural practices. and (d) studies of fireecologv. Aerogranhic (black-and-white) infraredfilm also shows differences between burned andunburned areas more readily than panchromaticfilm. This preliminary evidence forms the basisof the present paper.

LIMITATIONS OF PANCHROMATIC FILM IN

BUSHFIRE MAPPING

The relative limitations of panchromatic filmand the respective advantages of other film, espec-ially colour and false-colour aerial film. can bedemonstrated with reference to the severe Dan-denong Range bushfire of 14-17 January 1962and the subsequent regeneration of the forest.Immediately following this summer fire, aerialphotographs, using panchromatic film, were taken.

These were intended to serve as an accurate andrapid record of the extent and damage caused bythe bushfire. Panchromatic film records all wave-lengths of reflected radiation within the visiblespectrum. The film emulsion is sensitive to radia~tion in the 400 to 700 nm. range. Aerial panchro-matic film is always used with a minus-blue filter,such as a Kodak Wratten 12, which cuts out wave-lengths from 400 to 500 nm. This reduces Ray-leigh scattering and eliminates 'noise' without sig-nificantly reducing background information. Thus,panchromatic minus-blue photography records allvisible wavelengths from 500 to 700 nm. Conse-quently, many features that may differ significantlyfrom each other in their spectrazonal signatures- for example, the wavelengths of the peak reflec-tions - may have almost identical tones on pan-chromatic minus-blue films because the integratedresponse over the entire spectral region is the sameor very similar. Such was, in fact, so with thebushfire areas in the Dandenong Range. Thepanchromatic minus-blue aerial photographs didnot consistently show clearly the differencebetween burned and unburned areas. It was diffi-cult to assess the bushfire perimeter and theamount of fire damage; it was impossible to iden-tify species (Fig. I). Ground surveys wererequired to map boundaries. In steep terrain ofdifficult access, errors in the accuracy of theseboundaries could be substantial.

The general results from bushfires in sclerophyllforests in Australia are twofold: (a) the scrubunderstorey is completely razed by fire leaving theground bare and (b) the forest tree dominants-almost exclusively of the genus Eucalyptus - arenot killed. However, the foliage is killed by theradiant heat from the ground fire, turns brownand remains on the tree for several weeks. Aboutone month after the fire many trees are largelydefoliated and the ground carpeted with the deadleaves. An important exception is the 'ash group'of Eucalyptus (e.g. Eucalyptus regnans, E. gigan-tea) which includes some of the most importantcommercial species of south-east Australia. Theseare easily killed by fire (Cunningham 1960. Coch-rane 1969).

The photographs were taken one week after thefire, when most leaves were present on bothburned and unburned areas. There were nomarked structural differences in the canopy. Simi-larly, the differences between spectral reflection

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98 PROCEEDINGS OF THE NEW ZEALAND ECOLOGICAL SOCIETY, VOL. 17. 1970

'.-~,~,. ,

FIGURE 1. Panchromatic minus-blue aerial photo taken immediately after theDandenong bushfire of January 1962. Differences between unburned (left) andburned (right) are difficult to detect. Boundary between these areas is shown by

black line. '

[Photo State Aerial Survey, Victoria, 1962]

of dead brown leaves of Ihe burnt areas and thedull dark-green of living Eucalyptu,v leaves,although obvious on colour photographs, werenot distinguishable on panchromatic minus-bluephotographs.

It is doubtful if any better results would havebeen achieved than that shown in Figure I if thephotography had been done about three or fourweeks after the fire, when many of the burnedtrees would have been completely defoliated, Thedense carpet of brown leaves covering the groundwould probably still have spectral reflectionvalues, similar to those of green foliage. Theresolution of the I: 10,000 photographs would nothave enabled one to identify individual trunks,although large dead trees (stags) can be separatedfrom trees in full leaf.

Panchromatic minus-blue acnal photographs, jftaken several months after the fire, could probablybe used by a skilled interpreter to distinguishbetween burned and unburned areas on the basisof the reproduction,.of their textural differences.Thus the unburned areas with forest canopy wouldbe different from the bare soil and regeneratingscrub understorey. However, I have shown (Coch-rane 1966, 1968c) that simple clear-cut differences

are often not present because of very different anddistinctive regeneration patterns between treespecies and their associated undergrowth. In someareas regeneration of trees would result in texturalcharacteristics not greatly different from forest.Some areas of bare soil and leafless trees couldprobably be detected on tonal and textural varia-tions. Thus, differentiation between burned andunburned areas would still be difficult.

.

If spectrophotometric curves of burned andunburned bush could be measured, differences inspectral reflection could be used. Burned and un-burned areas Ihen could be detected photographic-ally on panchromatic film, by using suitable filtersto emphasise the spectral regions of greatest differ-ence and to .eliminate the regions of no difference.Such a procedure would have to be tested to deter-mine its practical validity for bushfire studies.

Is such experimentation warranted, however.when these results may be achieved so readilyfrom colour and false-colour photography? Meyerand Trantow (1961), in examining tonal differ-ences in conifers and deciduous trees in northernMinnesoa, found variable-filter photography wasinferior to colour infrared photography with aminus-blue filter. Recently, Carneggie and Lauer

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(1966) and Lauer (1969) have successfully usedspectrazonal aerial photography to identify trees.Recent tests I have made with panchromatic filmand minus-blue, minus-green, and minus-redfilters on both living and dead, but not burned,foliage of blue gum (Eucalyptus globulus) andmanna gum (E. viminalis) gave rather unsatisfac-tory results, Colour and false-colour photographstaken at the same time showed the differencesmore effectively.

BLACK-AND-WHITE INFRARED FILM

Black-and-white infrared or Aerographic infra-red film records wavelengths from 400 to 900 nm.With the exception of a noticeable dip at 500 nm.it can record both visible (400-700 nm.) and nearinfrared (700-900 nm.) reflection. When usedwith a Wratten 89B filter it records only infrared.Within this spectrum of electromagnetic energythe different reflection between dead and livingtissue of the burned and unburned forest is sub-stantial. This film could be used for mappingburned and unburned vegetation in Australianforests, but would show less total detail thanpanchromatic film because of poorer resolution.Thus, although Carneggie, Draeger and Lauer(1966) and other workers have clearly demon-strated the superiority of black-and-white infraredfilm over panchromatic minus-blue film for dis-tinguishing between burned and unburned conifer-ous vegetation it is not widely used.

COLOUR FILM

No aerial colour photographs were taken in theDandenong Ranges but ground photographs usingcolour film demonstrate the high potential ofcolour photography for studies of forest fires.Kodachrome and Ektachrome film showed dearlythe difference between the dun-brown of burnedforest and the greens of unburned forest. On aerialcolour photographs supplied by Carneggie, thebrown of a burned area near Russian River, Cali-fornia contrasting clearly with the green of un-burned vegetation. indicates the potential valueof aerial colour photography.

Previously, true colour has been difficult toachieve with Aerial Ektachrome colour filmbecause of haze, filter and exposure problems.However, the many subtle differences of hue,value and chroma recorded enable many more

features to be interpreted than is possible on eitherpanchromatic minus-blue or black-and-whiteinfrared film alone. Small-scale aerial colourphotography can yield more accurate informationthan comparable pan minus-blue photography(Tarkington and Sorem 1963, Sorem 1967).Anson (1966) demonstrated that, not only doescolour photography enable one to interpret morecategories or classes than on comparable panminus-blue photography, but much more detailcan be deciphered and more positive identificationof features made. Lauer (1966) found that iden-tification of tree communities made from aerialcolour transparencies were significantly moreaccurate than those made from aerial black-and-white prints. Although these interpretations werechiefly of different genera and thus more simplethan identification between different Eucalyptusforest communities, some of his divisions werebetween species of one genus.

The problem of haze with colour film takenat altitudes above 10,000 ft. may well be solvedwith the introduction of a negative-positive sys-tem. In this process, developed in Australia in1966-67, haze is filtered out at the time of proces-sing, not at the time when the photographs aretaken. Results with the introduction of this systemshowed good colour balance in a special trialat altitudes ranging from 5,000 ft.-25,000 ft. Bluehaze was effectively eliminated (Sims and Benson1967). These authors recognise colour negativesystems, such as MS Ektachrome 2448, as beingsuperior to conventional Aerial Ektachrome foridentification of Australian forest species.

Because tonal and textural differences areusually enhanced by colour variations, AerialEktachrome clearly differentiates between treeand scrub cover. Subtle differences aid in int~r~preting tree species, tree density, tree and scrubdensities, tree heights and classes of forest. Atlarge scales, this film is useful for distinguishingbetween healthy and diseased or damaged trees(Carneggie, et al. 1966). Benson and Sims (1967)recognised its value for such purposes in Austr'a-lian forestry. Colour infrared (false-colour) filmis more widely used for this purpose (Norman andFritz] 965; Meyer and French 1966, 1967; Knip-ling ]967; Weber and Olson 1967), although Ben-son and Sims refute its value for studies of Aus-tralian vegetation. Their refutation may resultfrom incomplete understanding of certain prob-

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100 PROCEEDINGS OF THE NEW ZEALAND ECOLOGICAL SOCIETY, VOL. 17, 1970

lems inherent in the use of such film (Cochrane,1968b).

Aerial photography using Aerial Ektachromecolour film would have recorded sharply andaccurately the boundaries of the Dandenong bush-fire. Even small areas of green trees that escapedburning may be expected to be readily identifiedbecause of sharp colour contrast. Experimentalphotography in the Plumas National Forest inthe Sierra Nevada Mountains of California, hasdemonstrated the potential value of high altitude,small scale, aerial, colour photography for map-ping wildfire boundaries 1'Carneggie et al. 1966).

Similarly, colour film would also record differ-ences between intensities of bushfires. A largebushlire rarely burns evenly over a large area.This was particularly true in the Dandeuong fire,and the same has been observed in many bushlireareas I have investigated over the last 10 years.Intensity of burning varies with many factors(Cochrane 1963) and ranges from severe burning,to light burning aud defoliation from radiant heat(Cochrane 1966, 1968c, 1969). In AustralianEucalyptus forests, such as in the DandenongRange, leaves are burned in areas of most severelires. On true colour photographs such areas showas black rather than the brown of areas where fireresults in death of leaves from radiant heat. Thesedifferences could not be detected on the aerialpanchromatic minus-blue photographs (Fig. I),but showed readily on ground colour photographs.Panchromatic photographs, taken on the groundimmediately following the Dandenong fire, didnot show these differences in panoramic views.Differences were difficult to observe even inground panchromatic photographs taken at closerange.

Colour film such as Aerial Ektachrome is betterthan either black-and-white infrared or panchro-matic minus-blue film for identification of treeswith foliage of similar density or scrub with similartexture (Anson 1966). If infrared reflection issimilar these cannot be distinguished on black.and-white infrared photography. Subtle colourdifferences between species can often be used incolour film to identify and map plant communitiesor specIes.

Aerial colour photographs would be most valu-able taken directly after a fire when contrasts incolour between burned and unburned vegetation\' onld be most marked. Its great superiority over

panchromatic minus-blne photography for dis-tinguishing between burned and unburned areaswarrant its testing and, if satisfactory, its wideuse in Australia. Accurate delimitation of burnedareas would be valuable for assessing extent ofdamage and for planning prescribed burning toreduce dangerous accumulations of ground fuelwhere such silvicultural control methods are con-sidered practical or economic (Hodgson 1967).No published results of the use of true colouraerial photography taken after the 1967 Tasman-ian bushfire are available. However, the use oftrue colour aerial photography rather than pan-chromatic suggests that wider use of colour photo-graphy techniques is imminent.

AERtAl. COLOUR PHOTOGRAPHY AND THE MAPPING

OF FOREST VEGETATION

I have drawn attention to the grave delicienciesin the fundamental description of vegetation with-in Australia (Cochrane 1967). Only a small per.centage of the continent's plant communities havebeen fully described ecologically. This appliesespecially to much of the sclerophyll forest. De-tailed species distributions are virtually unknown,particularly where such forests are found on roughdissected country. Accurate maps of distributionsare not likely to be produced by conventionallield mapping methods in such difficult country.

Colour aerial photography, if used at key timesfollowing bushfires can contribute information on(I) forest composition and (2) the ecology offorest dominants and of understorey speciesfollowing fires.

The Eucalyptus dominants of the sclerophyllforests exhibit remarkably distinct regenerationpatterns following bushfires. Species differ in thetime of appearance, rate, vigour, form, density andcolonr of the regenerating foliage (Cochrane1968c). Although it is true that regeneration pat-terns are affected by the severity of fires, seasonalconditions and geographical locations, the distinc-tive regeneration patterns of the species were notmasked by these factors in the Dandenong Raugestudy area. Thus. if aerial colour photographswere taken after the fires at successive timescorresponding to the known times of significantstages in the regeneration of the Eucalyptusspecies, it may well prove that accurate detailedmaps could be made of distributions. Detailed

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ground surveys I have made indicate that.in theOandenong Range, aerial colour photographs

taken between one and two monfhs after the firewould have shown very distinctive and vigorousregeneration from dormant epicormic shoots pre-sent on three species - the long-leaved box (E.elaeophora), mountain grey gum (E. gon/ocalyx),and narrow-leaved peppermint (E. rad/ala).

The former two, with blue-green (glaucous)juvenile leaves, can be easily distinguished fromthe latter with its light green foliage. Waxes pre-sent on the juvenile foliage of long-leaf box andmountain grey gum increase the peaks of reflectionin the visible spectrum (e.g. 5% to 10% at537 nm.). Although certain eucalypts frequentlypresent a different appearance on vertical colouraerial photographs from that expected from know-ledge of the species on the ground, this separationcould be made readily on the basis of colour alone,even if the hues in the aerial photographs differedfrom the distinctive ground colours. Distinguish-ing between the two former species, would notbe difficult as they both have strongly contrastedtree forms and habitat requirements. Areas ofthese species would show clearly against thestringybarks which do not regenerate so soon.These differences could not be detected on pan-chromatic (black-and-white) film.

Another series of photographs, using colourfilm, and taken seven months after the fire, wouldshow dark, greenish-red, relatively sparse regen-eration of the messmate stringybark (E. obi/qua).The different colour, the less dense foliage, thedifferent tree form and the concentration of regen-eration along upper surfaces of main brancheswould allow easy identilication of this species.The other stringybarks of the area - brownstringybarks (E. baxter/) and red stringybarks(E. macrorrhyncha) ~ would show clearly as

dark areas with no green growth. It would be diffi-cult to distinguish these two species from oneanother by leaf regeneration patterns on colourphotography taken when regeneration had begun.

Regeneration of undergrowth is largely absentunder these stringybarks for the Iirst six monthsbut is present later. It is difficult to distinguishsparse tree regeneration from u-nderstorey vegeta-tion in aerial photographs. However, by applyingecological principles in interpretation ~ these two

species exhibit very distinct habitat preferences ~

boundaries could probably be drawn fairly accur-ately.

Thus, two sets of aerial colour photographs ofthe burned area taken two months and sevenmonths after the fire give real promise of provid-ing sufficient information to map the vegetationdistributioncapidly and more accurately thanpreviously. To achieve a similar map by groundsurveys would involve much time and staff. Inaddition, the. finished ground survey map wouldprobably lack the accuracy and exact detail ofthe .aerial photographs.

The limitations of such procedures would notresult from technical problems of photographybut from the lack of information concerning pat-terns of regeneration after fire. More informationis required on the ecology of many species of thesclerophyll forests after fire so that informationon aerial colour photographs may be correctlyinterpreted. Variable epicormic emergence withina species because of. altered site or altitude, orboth, latitudinal location, fire intensity and numer-ous other factors would have to be consideredin selecting optimal times for aerial photographyin other places. For the Dandenong Range, whichis an area of mixed species, mixed age stands andvaried habitats (Cochrane 1968a, 1969), the timessuggested would provide maximum information.

COLOUR INFRARED FILM

Colour infrared photography (also called false-colour, Ektachrome Infrared Aero, and InfraredEktachrome photography and formerly knownas camouflage detection photography) oftenyields a wider variety of multi-spectral inform-ation than colour film. This has been demon-strated in several studies, particularly thoseby Anson (1966), Carneggie et al. (1966),Carneggie and Lauer (1966), Meyer and French(1966, 1967). Fritz (1967), Lauer (1968) andCarneggie (1968). It is one of the most usefulsingle remote sensing devices and is useful fordetailed field research and for medium and highaltitude studies. Recent investigations by Peaseand Bowden (1968. 1969) indicate that it maybe exceedingly useful for mapping programmesfrom space.

The film is sensitive to radiation in the blue,green and red portions of the visible spectrumas' well as in the near-infrared region. A minus~

blue filter is always used to exclude wavelengthsshorter than 500 nm. Thus, images on colour infra-red photographs result. from reflection from both

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102 PROCEEDINGS OF THE NEW ZEALAND ECOLOGICAL SOCIETY, VOL. 17. 1970

the near-infrared (700 to 950 nm.) and the greenand red (50J.--700nm.) portions of the solar spec-trum. Actively growing vegetation has a plateau ofmaximum rellection in the near infrared at 700-950 nm. This activates the infrared sensitive dyewhich produces red in the processod film (Fritz1967). Infrared colour photography, particularlywhen enhanced by the use of appropriate filters,records the most subtle differences between grow-ing vegetatiou (Pease and Bowden 1969). Thiscan frequently be used to identify different spociesvery accurately. In addition, the technique is oftenuseful for distinguishing between species that looksimilar in colour but which have very differentinfrared spectra. Thus, one species may appearas a lighter 'blush' than the other on false-colourIilm.

Angle of sun, light intensity, plant geometry,leaf incidence and plant vigour all affect infraredreflection. In addition, ground infrared photo-graphs of vegetation may show a different patternfrom aerial photographs of the same. Despite theseproblems, I have used false-colour film success-fully for vegetation studies in a wide range ofenvironments, including Australian and NorthAmerican deserts, forests of California. Oregon.New York and Florida, South-eastern Australiansclerophyll forests, New Zealand mixed podo-carp-broadleaf forests and Canadian tundra.

Infrared colour film gives sharper images thanother films when haze is present. This is animportant advantage. It is therefore much clearerthan colour photography for distant views,although some of the haze and resolution limita-tions of colour film have beeu rectified by therecent development of the negative colour systemmentioned earlier. This distinction applies particu-larly to small-scale colour infrared photography.i.e. filming from high altitudes. There is negligible(or very little) Rayleigh scattering of the longerwavelengths to which this infrared film is sensitive;and. in any event, it is less than that of the shortwavelengths to which colour Iilm and most otherfilms are sensitive.

Infrared colour photography using Kodak Ekta-chrome Infrared Aero Film. Type 8443 (Ekta-chrome Infrared Aero, false-colour Infrared Ekta-chrome or Ekta-Aero Infrared Iilm) would beexcellent for mapping bushfire boundaries. Thecolours - red for unburned bush and blue tocharcoal grey for the burned area - enhance

boundary differences because of their unusual(false) character. The contrast is greater than thatbetween brown and green on true colour film.Living vegetation has a high infrared reflectivityand shows red. The dead leaves absorb infraredand thus have a low reflection; they show bluish-black.

In a series of air photo studies of the vegetationat San Pablo Reservoir and at the MeadowValley-Buck Lake Area, California, at scales from!: 2,500 to I: 30,000, Lauer (1966) found colourinfrared more useful than colour film for the con-sistent identification of species. Both were vastlysuperior to black-and-white infrared and panchro-matic minus-blue Iilm. Tarkington and Sorem(1963) earlier emphasised some of the uses offalse-colour film for aerial photography. Fritz(1967), who made brief reference to the techniqueof optimising for the wavelength required withpanchromatic Iilm and Iilters, pointed out thatbetter results can be achieved more readily withthe use of aerial infrared colour film. Sims andBenson (1966). while emphasising the potentialof true colour aerial photography for identifica-tion of Australian forest trees, recorded themarked superiority of false-colour film for studiesof burnt vegetation.

Anson's (1966) comprehensive and detailedcomparison of aerial panchromatic minus-blue,colour. and infrared colour photographs alsodemonstrated the advantages of the latter formaximum detail and greatest range of categoriesfor mapping. Recently, I was able to consistentlydistinguish between individuals of two spocies ofEucalyptus-E. globulus and E. vimin~/is-in Cali~fornia. on colour infrared film at scales ofI : t0,000. This was more difficult on similar scaleAero Ektachrome colour photographs. Within thelimits of the resolution cell, identification, withalmost the same degree of accuracy, was possibleon I: 30,000 infrared photographs. Identificationsmade on photographs were all verified in the field.Additional variations in infrared reflection ineucalypt communities shown on the t: 10.000colour infrared photographs. when checked in thefield, corresponded with differences between ageand composition. J\1ature. even-age stands, irregu-lar mixed stands and regeneration variations withdifferent ratios of seedlings, saplings and polesof eucalypts. all had specific recognisable signals.Thus it appears that infrared colour Iilm would

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COCHRANE: COLOUR AND FALSE-COl.OUR AERIAL PHOTOGRAPHY FOR MAPPING VEGETATION

be very useful in studies of Australian bushfireecology. ,'-""" 'w

The regeneration patterns discussed earlier that

followed the J962 bushfire would show up on. .

infrared co]our photography at least as clearlyas on colour photography. Most studies of vegeta-tion on infrared colour photographs have beenmade in the northern hemisphere. Little has beenpublished on infrared colour studies of evergreen,sc1erophyllous, isobilateral leaves of .the Austral-ian forests or, indeed, of southern hemisphere andtropical vegetation. Exact parallels with nort~ernhemisphere evergreen conifers and broadleafdeciduous plants cannot be made. Howard (1966)has shown that four species of Eucalyptus, allfound in the Dandenong Range, namely, E. gonio-calyx, E. elaeophora, mountain ash (E. regnans)and the stringybark (E. obliqua) all have highbut not identical infrared reflection. Thus differ-ences on infrared colour Iilm between these specieswould result largely from a combination of thehigh infrared reflection and from differences inreflection of green and red visible light. The dark-ish glaucous regenerating leaves of E. goniocalyxand of E. elaeophora shows as a darker red-similar to evergreen conifers on infrared colourIilm - than those of the willow-like, paler greenleaves of E. radiata. The latter show as a brightred similar to that recorded by broadleaf decid-uous foliage. Juvenile leaves of stringybarks,which have a lower absorption of visible red thanthe other leaves, show as orange-red on colourinfrared Iilm.

Discriminating between tree and understoreylayers is often easier with infrared colour photo-graphy than with colour photography. The formeralso provide~ a greater contrast between vegeta..tion and soil than does colour film. although itis less valuable than the lattcr for distinguishingsoil types (Anson 1966). The use of infraredcolour photography would have been equally, oreven more, useful than colour photography forrecording regeneration stages and mapping speciesdistribution following the Dandenong bushfire.Infrared colour aerial photographs taken immed-iately after the fire would record sharply andclearly differences between burned and unburnedvegetation. The former would show as blue toblue grey; the latter as red. Intensity of burningcould be analysed by the amount of bare groundshown and by the variations between bluish-greenor, perhaps. shades of yellow (Benson and Sims

103

1967; Cochrane 1968b) shown by lightly burnedareas and the bluish-blacks - of severely burnedareas with much charcoal, dead leaves and fireash. Boundaries between-burned communities andsmooth-harked trees such as E. goniocalyx andE. regnans and between the fire-blackened andcharred, fibrous-barked stringybarks and black-ened, charred, rugose-barked long-leaved box andnarrow-leaved peppenriint, could possibly also bemade' on colour infrared imagery taken at thistime.

' ,

These features aud the"regeneration patternsdiscussed. under colour photography would all bedetectable on colour, infrared, photography takenbetween one and two months after the fire. Thevigorously regenerating juvenile leaves clothingthe trunks of E. goniocaly'x, E. elaeophora andE. radiata would show distinctly as various redscontrasting

_'with those of the adjacent burned

ground Or non-regenerating stringybarks. Thepattern and the colour of regenerating leaveswould show as a different red from the livingunburned foliage, as juvenile and adult EucalYPtu"foliage have different spectral responses. Some ofthe reasons for this are discussed more fully else-where (Cochrane I968b): See also Knipling(1967).

. ,

Photographs taken' about seven months afterthe bushfire would have been valuable for identify-ing burned stringybark communities from adjacentcommunities in the Dandenong area. At this stagemuch bare ground would be present in the stringy-bark communities because of their sparse regener~ation and the lack of undergrowth. Other com-munities would have most ground covered bvregenerating understorey. Infrared colour aerialphotographs have not been taken of bushfire areasbut accumulating evidence suggests that such filmscould probably record the many subtle regenera-tion patterns - varying from bare ground, grass,fern and xeric and mesic shrubs - which are notobvious on panchromatic minus-blue aerial photo-graphs. Such infrared colour photography wouldsave many'hours of field investigations, allowingtime to be 'devoted to detailed studies rather thanto reconnaissance mapping and sampling later.

Discrimination between species with similarappearance could 'probably be achieved fromsubtle colour variations by using colour compen-sation Iilters. Fritz (1967) and 'Pease and Bowden(1968, 1969) have demoustrated that much addi-tional information can be recorded by slight. mod-

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104 PROCEEDINGS OF THE NEW ZEALAND ECOLOGtCAL SOCIETY, VOL. 17, 1970

erate or great enhancement of infrared imagery byusing such Iilters. The techniques developed areparticularly useful for small-scale aerial photo-

gmphy. These workers believe that such film haspotential for universal use.

Truly accurate mapping of the distribution ofAustralian sclerophyll species from photo-inter-pretation, however, is dependent upon a soundknowledge of the ecology of such forests afterfire. Furthermore, this knowledge is vital if theannual destruction and loss of resources frombushfires is to be arrested or at least better con-trolled. To date there have been insufficient inves-tigations of this topic. Studies of mountain ash(Cunniugham 1960, Cochrane 1969), make anotable exception. Other useful contributions havebeen made by Lawrence (1939), Gardner (1956),Gilbert (1959), McArthur (1962), King (1963),Hodgson (1967) and Cochrane (1963, 1968c).but much remains to be done.

Sclerophyll forests are made up of many dif-ferent associations which reflect the many differ-ences in rocks. soils. climatic and biotic factors.Very varied patterns are present in broken, dis-sected country where many such forests are found.Studies of the ecology of sclerophyll forests showthat fires do follow a broadly predictable pattern.Oifferences in structure (Cochrane 1968a), inunderstorey composition, in pattern of burning,and in degree of lire tolerance, all exert importantinfluences upon bushfire patterns. Both the formand rate of vegetation regeneration after bushfires(Cochrane, 1966, 1968c), when known, contributeto a better understanding of vegetation-fire rela-tionships and possibly. if wisely used. to betterbushfire control in the future. Many of thesevegetation-fire relationships could be obtainedfrom aerial colour infrared photography.

ACKNOWLEDGMENTS

This study received partial support from the U.S.Geologie<tl Survey, Geographic Applications Program,through Contract No. USGS 14-08-001~10848 for theNational Aeronautics and Space Administration.

The author is indebted to Dr Robert Colwell, Mr DonLauer, and to Me David Carneggie, School of Forestry,University of California, Berkeley, for advice, for makingavailable infrared colour photographs of San PabloReservoir and for kindly reading the manuscript. Than;';'sare also due to Dr Robert Pease and Dr Loonard Bow-den, Department of Geography, University of California.Riverside, for helpful discussion. Special thanks are due

to Dr David Simonett. Center for Research in Engineer-in Science (CRES) Remote-Sensing Labo:-atory, Univer-sity of Kansas. Lawrence, for his assistance, enthusiasmand constructive ideas during the preparation of this

paper.

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