Air Photo Interpretation Research Articles

TOPOGRAPHIC MAPPING SUPPORT IN THE SOUTH AFRICAN MILITARY DURING THE 20TH CENTURY

Maps provide a base for all intelligence operations and strategic and tactical decisions, supporting the planning and execution of all battlefield functions. The development of military mapping support in South Africa, related closely to the development of aerial photography, may be divided into five, sometimes overlapping, phases. The first of these phases spans the years from 1840 to 1930 and is characterised by the gradual recognition that aerial photographs could be used for mapping. Two major conflicts – the Anglo Boer War and the First World War – marked this development. The Second World War is the key event of the second phase (1930–1950), which witnessed a rapid expansion of aerial photo coverage. The third phase (1945–1960) saw the overemphasising of interpretation techniques rather than the analytical use of results, which was rectified during the fourth phase (1955–1962) when the focus shifted to the applied uses of air-photo interpretation. During the third and fourth phases the topographic mapping support ability of the South African military was expanded. The fifth phase (since 1960) commenced with the expansion of data gathering and analysis into portions of the electromagnetic spectrum beyond the small visible sector. During this period the protracted nature of the conflict on the northern border of Namibia (formerly South West Africa) and the war in Angola focused attention on the South African military mapping system. The National Service system allowed for the expansion of mapping units and the thorough mapping of large areas adjoining our borders. Through all five phases, mapping in the South African military has advanced from hand-produced maps to the utilisation of complex equipment that satisfies the sophisticated mapping needs of a modern defence force. This paper presents a brief history of both mapping support and the mapping units that have served within the South African theatre during the twentieth century. In doing so, the operational importance of topographic maps is also highlighted.

Ecosystem classification and inventory maps as surrogates for ground beetle assemblages in boreal forest

AIMS: We compare performance of ecosystem classification maps and provincial forest inventory data derived from air photography in reflecting ground beetle (Coleoptera: Carabidae) biodiversity patterns that are related to the forest canopy mosaic. Our biodiversity surrogacy model based on remotely sensed tree canopy cover is validated against field-collected ground data. METHODS: We used a systematic sampling grid of 198 sites, covering 84 km2 of boreal mixedwood forest in northwestern Alberta, Canada. For every site, we determined tree basal area, characterized the ground beetle assemblage and obtained corresponding provincial forest inventory and ecosystem classification information. We used variation partitioning, ordination and misclassification matrices to compare beetle biodiversity patterns explained by alternative databases and to determine model biases originating from air photo-interpretation. IMPORTANT FINDINGS: Ecosystem classification data performed better than canopy cover derived from forest inventory maps in describing ground beetle biodiversity patterns. The biodiversity surrogacy models based on provincial forest inventory maps and field survey generally detected similar patterns but inaccuracies in air photo-interpretation of relative canopy cover led to differences between the two models. Compared to field survey data, air photo-interpretation tended to confuse two Picea species and two Populus species present and homogenize stand mixtures. This generated divergence in models of ecological association used to predict the relationship between ground beetle assemblages and tree canopy cover. Combination of relative canopy cover from provincial inventory with other geo-referenced land variables to produce the ecosystem classification maps improved biodiversity predictive power. The association observed between uncommon surrogates and uncommon ground beetle species emphasizes the benefits of detecting these surrogates as a part of landscape management. In order to complement conservation efforts established in protected areas, accurate, high resolution, wide ranging and spatially explicit knowledge of landscapes under management is primordial in order to apply effective biodiversity conservation strategies at the stand level as required in the extensively harvested portion of the boreal forest. In development of these strategies, an in-depth understanding of vegetation is key.

白馬岳東麓，長走沢・金山沢の地すべり地形と堆積物

This paper describes landslide features observed in the Nagashirisawa Basin and Kanayamazawa Basin east of Mount Shiroumadake (central Japan), where mid- to late-Pleistocene mountain glaciers are thought to have developed. Geomorphological analyses accompanied by a study of airphoto interpretation and a geological survey show gentle slopes, low-relief ridges and mounds in the basins. In most cases, angular gravels in major deposits of these landforms comprise either one or a few kinds of bedrocks exposed near the slopes. No gravels originating from any other geology in the basins are found. Jigsaw-brecciated clasts and folded-elongated silt patches in the major deposits can also be distinguished. Landslide processes, including the gravitational deformation of bedrock (i.e., mass rock creep), are probable causes of these features. Chronological information suggests that a major landslide occurred during the period from late Pleistocene to late Holocene. The triggers of these landslides remain incompletely understood, glacial–interglacial climate changes along with precipitation variations, as well as paleoearthquakes originating from nearby active faults, might be important. Some landslides found in the basins overlap moraines identified by previous research. Historical geomorphology of this area requires further study.

An object-based approach for flood area delineation in a transboundary area using ENVISAT ASAR and LANDSAT TM data

The aim of this study was to develop a straightforward approach for flood area mapping in a transboundary riverbed using Geographic Object-Based Image Analysis. Weak bilateral/multilateral cooperation among neighboring countries hampers effective disaster management and mitigation activities over transboundary areas and strengthens the demand for reliable remote-sensing-derived information. Three object-based classification approaches using ENVISAT/ASAR and multi-temporal LANDSAT TM data were developed and validated for flood area delineation. The accuracy assessment of the classification results was based on oblique air photo interpretation and an area-based comparison with the official flood map. The bi-level object-based model using the Normalized Difference Water Index and the original post-flood TM bands attained 92.67% overall accuracy in inundated-areas detection, while the ENVISAT/ASAR classification was the least accurate (85.33%), probably due to the lower spatial resolution of the Synthetic Aperture Radar image. A strong agreement (92.14%) was found between the LANDSAT flood extent and the official flood map, suggesting that the proposed method has the potential to be employed in the future as a standard part of a flood crisis management process.

Image-based predictive ecosystem mapping in Canadian arctic parks

Ecological monitoring of Arctic national parks is challenging owing to their size and remote locations. Baseline ecosystem maps are a basic requirement for monitoring and are often derived from classification of remote sensing data. In many cases, however, the vegetation communities of interest overlap spectrally and cannot be separated using imagery alone. One solution is to use ancillary spatial data that are able to predict the distribution of Arctic ecosystems, which are often structured along environmental gradients. This paper presents a new image-based predictive ecosystem mapping (I-PEM) method that integrates remote sensing-based vegetation mapping with predictive terrain attributes from a digital elevation model. The approach is unique in its use of a conventional, air photo-based ecosystem map to train a decision tree classifier for mapping over a larger area of satellite coverage. I-PEM is demonstrated using SPOT HRVIR imagery over Ivvavik National Park in Yukon and Torngat Mountains National Park in Newfoundland. Results indicate that a 28-class ecosystem map derived from air-photo interpretation can be reproduced using the method with 85% or greater accuracy.

A PRELIMINARY APPROACH TO THE PARTICIPATORY MICRO WATERSHED LAND-USE SURVEY METHOD ON THE BASIS OF AIRPHOTOS

This paper deals with the Participatory Micro Watershed Land-use Survey Method on the Basis of Airphotos in the Sino-Germany joint micro-watershed development project Sustainable Development of Mountainous Area in Jiangxi. It gives a preliminary description of the basic concept and the preparatory work of the base map for field survey and the whole mapping procedure for this project, which includes establishment of participatory land-use classification system, in-room pre-judgment and interpretation of airphotos, field mapping and selection of standard interpretation areas, holistic interpretation and field verification, digitization, editing and printing. The case study was conducted all the way at the Huangling micro-watershed in Luojiang town of Yudu County, Jiangxi Province. The advantages and disadvantages of the method are analyzed, with the hope of providing some reference for future similar work.

Comparison of GIS-based gullying susceptibility mapping using bivariate and multivariate statistics: Northern Calabria, South Italy

This paper presents GIS-aided procedures for the evaluation of gullying susceptibility on a statistical basis. Field surveys and air-photo interpretation allowed us to identify gullies, geology and land use, while some predisposing factors were derived from a 7.5 m cell-size DEM. In order to investigate the role of each instability factor in controlling the spatial distribution of gullies, we implemented four models that differ in the types of method (bivariate vs. multivariate), training set sampling (polygon or point-based) and variables (continuous or categorical). The models were applied to the Turbolo river catchment, a tributary of the Crati River, Northern Calabria, Italy. The susceptibility values were classified into five categories. Model performance was evaluated using prediction rate curves and by comparing the proportion of each susceptibility class with gully distribution in the validation set. Although all models showed relatively good performances, the bivariate method overestimated the extent of the high susceptibility classes. The multivariate logistic regression model using continuous variables was found to be the best model in predicting gullying susceptibility of the study area. The area classified as stable increased with DEM cell size, meaning that a reasonably fine DEM should be used.

Pemanfaatan Teknologi Penginderaan Jauh dan Sistem Informasi Geografis untuk Pendugaan Potensi Peresapan Air DAS Wedi Kabupaten Klaten-Boyolali

The study was conducted in Klaten-Boyolali regencies in Wedi Watershed which is the Watershed of Dengkeng. The study aimed to: 1) know the interpretation precision of black and white panchromatic air photo scaling 1: 50.000 in identifying the soil factor, slope, landuse, vegetation density, and land conversation, related to the influences toward potensial water infiltration in the area of study; and 2) to know the distribution of potensial water infiltration in the area of study and analyze to the spatial distribution. The method of the study used was air photo interpretation supported by limited survey for filed test. The method of analysis applied was spatial analysis using Geographical Information System Technology (GIS). The result of the study showed that: 1) the level of air photo for interpreting determination factor of water infiltration in the area of study is acceptable together with the precision level of: slope 89.47%; soil texture 82.14%; land use 90.16%; vegetation density 88.89%; and land conservation 80.88%. it meant that although the precision level achieved had not been included in very precise category, the air photo still can be used in this study; 2) the potensial of water infiltration in the area of study tended to be less good, indicated by the dominance of the land in status of ‘begin to be rather critical and critical’ in the width of 81.999 km² or 75.04% placed by 28 land units; while the remaining of 8 land units in the width of 3.154 km² or 20.62% was in the status of 'natural normal' and 14 land units in the width of 22.544 km² or 20.62% had ‘good’ status. In the area of study, the space of land units with the potensial of good infiltration had no spatial relevance to the space of land units and the great infiltration capability.

Cosmogenic radionuclide dating indicates ice-sheet configuration during MIS 2 on Nordaustlandet, Svalbard

Hormes, A., Akcar, N. & Kubik, P. W. 2011: Cosmogenic radionuclide dating indicates ice-sheet configuration during MIS 2 on Nordaustlandet, Svalbard. Boreas, 10.1111/j.1502-3885.2011.00215.x. ISSN 0300-9483.0300-9843 Glacial geological field surveys, aerial image interpretation and cosmogenic radionuclide (CRN) dating allowed us to reconstruct the ice-sheet configuration on Nordaustlandet, the northernmost island of the European sector on the margin of the Arctic Ocean. The timing of deglaciation was investigated by determining the 26Al and 10Be ages of glacially scoured bedrock, weathered periglacial blockfields and glacial erratic boulders. Only 10Be ages were useful for our interpretations, because of unresolved analytical problems with 26Al. Fjords and lowlands on Nordaustlandet yielded Late Weichselian 10Be ages, indicating that actively erosive ice streams scoured the coastal fjord bathymetry during marine isotope stage (MIS) 2. In Murchisonfjorden, ground-truthed air-photograph interpretation and 10Be ages of boulders indicated a cold-based glacier ice cover during MIS 2 on higher plateaus. 10Be ages and lithological studies of erratic boulders on higher and interior plateaus of Prins Oscars Land (>200–230 m a.s.l.) suggest that the Mid-Weichselian glaciation (MIS 4) might have been more extensive than that during MIS 2.

Historical Land Use and Plant-Community Variability in a Wisconsin Calcareous Fen

In 2008 a calcareous mound fen not listed in the state Natural Heritage Inventory was discovered in south-central Wisconsin. Air photo interpretations and interviews with land users indicated two distinct major historical alterations to this fen: (1) drainage tiling without widespread soil disturbance and (2) plowing with or without direct drainage. Nonmetric multidimensional scaling ordination of survey plots revealed that an assemblage of calciphiles, fen indicators, and wetland generalists persisted in the mound's center, while invasive herbaceous and woody vegetation reached highest cover along the disturbed flanks. Cluster analyses revealed three distinct communities: (1) a fen meadow in the center of the fen, (2) invading shrub-carr in tiled areas, and (3) a weedy/invasive herbaceous community where soil disturbance was widespread. This study lends support to past assertions that drainage can lead to shrub-carr invasion and suggests that widespread soil disturbance can lead to domination by herbaceous invasive plants on fen flanks.

Application and validation of bivariate GIS-based landslide susceptibility assessment for the Vitravo river catchment (Calabria, south Italy)

The Calabria (Southern Italy) region is characterized by many geological haz- ards among which landslides, due to the geological, geomorphological, and climatic characteristics, constitute one of the major cause of significant and widespread damage. The present work aims to exploit a bivariate statistics-based approach for drafting a landslide susceptibility map in a specific scenario of the region (the Vitravo River catchment) to provide a useful and easy tool for future land planning. Landslides have been detected through air-photo interpretation and field surveys, by identifying both the landslide detachment zones (LDZ) and landslide bodies; a geospatial database of predisposing factors has been constructed using the ESRI ArcView 3.2 GIS. The landslide susceptibility has been assessed by computing the weighting values (Wi) for each class of the predisposing factors (lithology, proximity to fault and drainage line, land use, slope angle, aspect, plan curvature), thus evaluating the distribution of the landslide detachment zones within each class. The extracted predisposing factors maps have then been re-classified on the basis of the calculated weighting values (Wi) and by means of overlay processes. Finally, the landslide susceptibility map has been considered by five classes. It has been determined that a high percentage (61%) of the study area is characterized by a high to very high degree of susceptibility; clay and marly lithologies, and slope exceeding 20 in inclination would be much prone to landsliding. Furthermore, in order to ascertain the proposed landslide sus- ceptibility estimate, a validation procedure has been carried out, by splitting the landslide detachment zones into two groups: a training and a validation set. By means of the training set, the susceptibility map has first been produced; then, it has been compared with the

Geomorphological map of the Crotone Province (Calabria, South Italy)

Please click here to download the map associated with this article. The geomorphological map described covers an area of about 1,720 km, located on the northeastern part of Calabria (south Italy); it contributes to the understanding of both long-term landscape evolution and present-day trends of the Crotone Province. The map, at a 1:75,000 scale, integrates information coming from geomorphological analysis of relief, air photo interpretation and fieldwork. It documents the interplay between tectonic and climatic controls at different temporal and spatial scales. Several remnants of planation surfaces, developed during late Miocene-early Pliocene, result from ancient landscape fragmentation and uplift since the Late Pliocene. Marine and alluvial terraces reflect complex cycles of erosion and deposition, possibly in relation to climate and tectonism during most of the Quaternary. Finally, the present landscape is heavily affected by slope denudational processes such as mass movements, running water processes and wave action. This map may provide the basis for further analyses, representing a useful tool for land management as well as the initial step for the assessment of geomorphological hazard and risk.

Geomorphology and GIS analysis for mapping gully erosion susceptibility in the Turbolo stream catchment (Northern Calabria, Italy)

This work summarizes the results of a geomorphological and bivariate statistical approach to gully erosion susceptibility mapping in the Turbolo stream catchment (northern Calabria, Italy). An inventory map of gully erosion landforms of the area has been obtained by detailed field survey and air photograph interpretation. Lithology, land use, slope, aspect, plan curvature, stream power index, topographical wetness index and length-slope factor were assumed as gully erosion predisposing factors. In order to estimate and validate gully erosion susceptibility, the mapped gully areas were divided in two groups using a random partitions strategy. One group (training set) was used to prepare the susceptibility map, using a bivariate statistical analysis (Information Value method) in GIS environment, while the second group (validation set) to validate the susceptibility map, using the success and prediction rate curves. The validation results showed satisfactory agreement between the susceptibility map and the existing data on gully areas locations; therefore, over 88% of the gullies of the validation set are correctly classified falling in high and very high susceptibility areas. The susceptibility map, produced using a methodology that is easy to apply and to update, represents a useful tool for sustainable planning, conservation and protection of land from gully processes. Therefore, this methodology can be used to assess gully erosion susceptibility in other areas of Calabria, as well as in other regions, especially in the Mediterranean area, that have similar morphoclimatic features and sensitivity to concentrated erosion.

Does interpretation of Marbled Murrelet nesting habitat change with different classification methods?

Accurate and reliable identification of potential nesting habitat is required to manage for the threatened Marbled Murrelet (Brachyramphus marmoratus). Three habitat classifications are typically used by wildlife planners: a bivariate suitability algorithm following recommendations of the Canadian Marbled Murrelet Recovery Team (CMMRT) and based on geographical information systems (GIS), and two habitat classifications based on air photo interpretation mapping and low-level aerial survey mapping. The CMMRT model uses vegetation resource inventory data. The air photo interpretation and low-level aerial survey methods directly assess the forest for attributes likely to provide nesting platforms, cover, and access into the stand by the bird. The prime indicators of nesting habitat potential for murrelets are large (generally mossy) branches for use as nest platforms. These are only directly visible using low-level aerial surveys. Methods involving GIS cost the least to apply, and low-level aerial surveys cost the most. We compared and assessed the consistency of the three methods using 243 sites. The CMMRT model proved least reliable by underestimating habitat suitability of sites compared to both the air photo interpretation and aerial survey estimates. The air photo interpretation and aerial survey methods were generally aligned in the ordinal ranking of sites by habitat class, but only 44% had matching ranks. Sites that differed tended to be ranked lower by air photo interpretation and mostly occurred in the “Moderate” and “Low” air photo interpretation classes. Either classification may refine information from the CMMRT model, particularly for habitat classed as “Unsuitable.” Using air photo interpretation first and then applying the aerial surveys as a further refined assessment of moderate and low habitat classes may provide the most cost-effective approach for accurately classifying and mapping habitat potential for management planning.

Geomorphological Map of the area between Frosolone and Trivento (Molise, Italy)

Please click here to download the map associated with this article. A 1:50,000-scale geomorphological map of the area between the settlements of Frosolone and Trivento (Molise Region, Italy) is presented and discussed in this paper. Field surveys and air photo interpretations allowed the characterization of the main morphological landforms of the study area, drawn from the reduction of an original 1:5,000-scale field map. The landforms have been grouped on the basis of the main controlling factors, as follows: i) tectonic and structural landforms; ii) slope landforms; iii) karst landforms; iv) fluvial landforms. This map shows the distribution of the geomorphic processes presently active, as well as the main relic landforms. Consequently, the collected data aim to provide a useful and easy tool for land planning policy; in addition, since the study area represents a typical geomorphic scenario of the southern Apennines, the data produced could be used in developing more widely-applicable landscape evolution models.

Mapeamento de anomalias de drenagem: indícios de controle litológico e estrutural na bacia hidrográfica do Cotia, em Cotia – SP, Brasil

Este trabalho busca analisar o cenário geomorfológico da bacia hidrográfica do Cotia, em Cotia (SP). O objetivo da pesquisa é a investigação da configuração da rede de drenagem do alto curso do rio em questão, localizado na Reserva Florestal do Morro Grande (RFMG), no qual são encontradas anomalias de drenagem, com destaque para uma sequência de inflexões de 90° no canal. A área de estudo está inserida regionalmente no planalto de Ibiúna, um compartimento geomorfológico constituído por morros e espigões alongados de média a alta declividade, com altitudes que variam de 860 a 1.075 metros. Essa unidade é composta por granitos, gnaisses e migmatitos neoproterozóicos, os quais poderiam indicar a influência de sistemas de juntas no traçado da drenagem. Além da influência litológica como potencial controlador dessa rede, há o fator estrutural, expresso pela ocorrência de falhas transcorrentes, integrantes da Zona de Cisalhamento de Caucaia, que atravessam o Cotia em direção NE-SW. Como métodos de investigação da área, foram adotadas técnicas de fotointerpretação e mapeamento digital (em escalas 1:25.000 e 1:50.000, respectivamente), com o intuito de identificar feições geomorfológicas que contribuam para a compreensão dos processos envolvidos na configuração atual dessa rede de drenagem.

Hydrological and geomorphological significance of rock glaciers in the dry Andes, Chile (27°–33°S)

AbstractThe latitudinal‐altitudinal distribution of rock glaciers in the dry Chilean Andes between 27° and 33°S was analysed and their hydrological and geomorphological significance evaluated. Statistical estimation techniques were used based on digital elevation models and air photo interpretation, and sediment budget models were applied to assess surface‐lowering rates. The estimated specific density of rock glaciers in the study area is 1.4 per cent, which corresponds to 147.5 km2 and a water equivalent of 2.37 km3. A comparison with glacier water equivalents derived from revised glacier inventory data shows that rock glaciers are more significant stores of frozen water than glaciers between 29° and 32°S. The latitudinal‐altitudinal distribution of rock glacier limits roughly follows the mean annual air 0°C isotherm, but in the southern part of the study area it extends into elevations where modern regional mean annual air temperatures exceed 0°C. High Andean surface‐lowering rates inferred from rock glacier sediment budget models are in the order of 0.6–0.7 mm yr−1, which is comparable to previous results from the dry Chilean Andes, but lower than in the more humid Andes further south. Copyright © 2009 John Wiley & Sons, Ltd.

An examination of controls on debris flow mobility: Evidence from coastal British Columbia

We characterize and consider controls to runout distance of debris slides and debris flows using 1700 field observations supplemented by air photograph interpretation from coastal British Columbia. We examine the role of slope on deposition and scour and determine that they occur on steeper and flatter slopes (respectively) than previously reported. Mean net deposition occurred on slopes between 18° and 24° for open slope failures and between 12° and 15° for channelized debris flows. We demonstrate a practical method for estimating both entrainment and runout in the field and in a GIS and provide an example entrainment map for Vancouver Island, British Columbia. We consider other controls to post failure landslide mobility, including the role of gullies and stream channels, roads and benches, and intact forests. Shallow landslides that hit streams and gullies at acute angles had a high probability of transforming into a channelized debris flow, whereas landslides that hit streams and gullies at obtuse angles did not. Forests played a substantial role in landslide runout: debris flows travelling through a logged slope deposited much of their load when hitting a forest boundary and stopped entirely within 50 m of that boundary in 72% of the cases examined. Roads also tended to stop or reduce the size of open slope debris flows in 52% of the cases. The results are expected to be useful to land management applications in regions with frequent shallow landsliding.

Assessing sustainability for global forests: a proposed pathway to fill critical data gaps

The UN’s Millennium Development Goals (MDGs) and other regional and national policy commitments have motivated an upsurge of interest in concepts and practical methods for monitoring forest conditions and trends at very wide geographic scales. Two approaches to sustainability assessment at a global level are reviewed here. One consists of monitoring change in forest conditions over time—the so-called Criteria and Indicators (C&I) approach. Another approach compares nations at a given point in time. An example is the Yale Environmental Performance Index (EPI). Both approaches yield insights. It is widely recognized, though, that severe data weaknesses afflict forest information over much of the world. These weaknesses include weak or absent information on wood consumption in many regions, poor area estimates, and weak or absent information on key ecological conditions in forests. The purpose of this essay is to introduce these efforts at global assessment, and to argue that an entirely new discipline is needed to supply the information needed. The focus of this new discipline would be to design an ecologically based set of definitions for forest and related ecosystems, and then to build and implement the optimum combination of satellite measurements, air photo interpretation, and field plot measurements needed to measure world forest resource conditions and trends. Examples of this new approach are already appearing. This argument is addressed to members of the global forest policy community concerned with assessment, and to scientists, technologists, and managers in the many technical fields already engaged on one or another aspect of measuring and monitoring forest conditions at a national and regional scale.

Relationships between habitat area, habitat quality, and populations of nesting Marbled Murrelets

We review relationships between the area and quality of apparently suitable nesting habitat (as defined by canopy structure) and the population size of Marbled Murrelets (Brachyramphus marmoratus) which such habitat might support. This information is important to manage the old seral forest nesting habitat of this threatened seabird. Studies at different spatial scales indicate that linear relationships provide good, biologically feasible fits between murrelet counts and areas of apparently suitable habitat when the effects of habitat quality are unknown. A large-scale analysis across Washington, Oregon, and California showed a strong linear relationship between murrelet numbers and area of habitat within large conservation regions. Seven separate watershed-level radar studies (six in British Columbia and one in Washington) support a linear relationship and also indicate that when logging reduces habitat, the murrelets do not aggregate in the remaining habitat at higher densities. Tree-climbing studies show similar trends at stand levels: compared to more pristine habitat, nest densities were not higher in remnant old-growth patches in depleted, highly fragmented areas. Do murrelets nest at higher densities in higher-quality habitat? The sparse information on this topic suggests a correspondence between nest locations and habitat quality as assessed by algorithms, air photo interpretation, and low-level aerial surveys. Most nests (92% and 86% in pooled data from aerial surveys or air photo interpretation, respectively) were found in habitat rated as Moderate, High, or Very High, and few (8% and 14%, respectively) in those rated Low, Very Low, or Nil. The relationship between perceived quality and the likelihood of nesting is, however, non-linear and it is premature to assume that murrelet nest densities will be significantly higher within the upper ranks of suitable habitat assessed from forest features.