John M. Kovacs

The application of small unmanned aerial systems for precision agriculture: a review

Precision agriculture (PA) is the application of geospatial techniques and sensors (e.g., geographic information systems, remote sensing, GPS) to identify variations in the field and to deal with them using alternative strategies. In particular, high-resolution satellite imagery is now more commonly used to study these variations for crop and soil conditions. However, the availability and the often prohibitive costs of such imagery would suggest an alternative product for this particular application in PA. Specifically, images taken by low altitude remote sensing platforms, or small unmanned aerial systems (UAS), are shown to be a potential alternative given their low cost of operation in environmental monitoring, high spatial and temporal resolution, and their high flexibility in image acquisition programming. Not surprisingly, there have been several recent studies in the application of UAS imagery for PA. The results of these studies would indicate that, to provide a reliable end product to farmers, advances in platform design, production, standardization of image georeferencing and mosaicing, and information extraction workflow are required. Moreover, it is suggested that such endeavors should involve the farmer, particularly in the process of field design, image acquisition, image interpretation and analysis.

Assessing mangrove use at the local scale

Abstract To evaluate the local use of mangrove forests, forty interviews were conducted with elderly fishermen from six villages in the Teacapan-Agua Brava lagoon–estuarine system of the State of Nayarit. Results indicate that the type of species is important to both the identification and local use of the mangrove forest. Overall, Laguncularia racemosa was identified as the species most frequently used in this region of Mexico, being employed quite regularly in the construction of tobacco galleries, stakes, poles, tapos (fish traps), fences and walls. By comparing the fishermens perceived potential use of Rhizophora mangle to its perceived actual use, it was found that this species had been employed as an important source for medicine and tannins. However, Rhizophora mangle is presently employed, and only periodically, for ceiling support in rural homes. Several key problems encountered in the evaluation of mangrove use at the local level are discussed.

Perceptions of environmental change in a tropical coastal wetland.

To assess whether local knowledge can contribute to the identification and evaluation of natural and anthropogenic disturbances in a mangrove forest, interviews were conducted with local fisherman of the Teacapan-Agua Brava lagoon–estuarine system of Mexico. The results indicate that an increase in water salinity, following the opening of an artificial canal, has resulted in a major disturbance in the mangroves of this region. Observations of changes in the fauna of the mangroves also coincide with this modification. The responses of the fishermen further suggest that the degree of impact from the salinity on the mangroves varies by species (e.g. Laguncularia racemosa is less tolerant than Rhizophora mangle). Other factors identified as inciting disturbances, but not previously reported for this system, include a hurricane and an infestation by caterpillars. According to the fishermen, the continued modification of the water salinity and hurricanes are the two greatest threats to the remaining mangroves. Copyright

Large-scale dieback of mangroves in Australia’s Gulf of Carpentaria: a severe ecosystem response, coincidental with an unusually extreme weather event

This study records and documents the most severe and notable instance ever reported of sudden and widespread dieback of mangrove vegetation. Between late 2015 and early 2016, extensive areas of mangrove tidal wetland vegetation died back along 1000km of the shoreline of Australia’s remote Gulf of Carpentaria. The cause is not fully explained, but the timing was coincident with an extreme weather event; notably one of high temperatures and low precipitation lacking storm winds. The dieback was severe and widespread, affecting more than 7400ha or 6% of mangrove vegetation in the affected area from Roper River estuary in the Northern Territory, east to Karumba in Queensland. At the time, there was an unusually lengthy period of severe drought conditions, unprecedented high temperatures and a temporary drop in sea level. Although consequential moisture stress appears to have contributed to the cause, this occurrence was further coincidental with heat-stressed coral bleaching. This article describes the effect and diagnostic features of this severe dieback event in the Gulf, and considers potential causal factors.

Multi-Temporal Polarimetric RADARSAT-2 for Land Cover Monitoring in Northeastern Ontario, Canada

For successful applications of microwave remote sensing endeavors it is essential to understand how surface targets respond to changing synthetic aperture radar (SAR) parameters. The purpose of the study is to examine how two particular parameters, acquisition time and incidence angle, influences the response from various land use/land cover types (forests, urban infrastructure, surface water and marsh wetland targets) using nine RADARSAT-2 C-band fine-beam (FQ7 and FQ21) fully polarimetric SAR data acquired during the 2011 growing season over northern Ontario, Canada. The results indicate that backscatter from steep incidence angle acquisitions was typically higher than shallow angles. Wetlands showed an increase in HH and HV intensity due to the growth of emergent vegetation over the course of the summer. The forest and urban targets displayed little variation in backscatter over time. The surface water target showed the greatest difference with respect to incidence angle, but was also determined to be the most affected by wind conditions. Analysis of the co-polarized phase difference revealed the urban target as greatly influenced by the incidence angle. The observed phase differences of the wetland target for all acquisitions also suggested evidence of double-bounce interactions, while the forest and surface water targets showed little to no phase difference. In addition, Cloude-Pottier and Freeman-Durden decompositions, when analyzed in conjunction with polarimetric response plots, provided supporting information to confidently identify the various targets and their scattering mechanisms.

Examining Local Ecological Knowledge of Hurricane Impacts in a Mangrove Forest Using an Analytical Hierarchy Process (AHP) Approach

Abstract To examine the observations of fishermen regarding the impact of a hurricane on a mangrove forest of the Mexican Pacific, twenty-two structured interviews using an Analytical Hierarchy Process (AHP) approach were conducted in four villages of the Teacapán-Agua Brava lagoon-estuarine system. The local fishermen were asked to assess the likelihood that a mangrove tree would not survive a hurricane based on three attributes: main stem condition, diameter of main stem and species. The results suggest a high degree of consistency amongst the villages and with the observations of a previous investigation using the traditional scientific data collection methods. With few exceptions, the fishermen indicated that large diameter trees were the most susceptible to hurricanes. Conversely, that black mangrove (Avicennia germinans) and an intact main stem condition would indicate a better likelihood of surviving such an event. From the results of this investigation, it is suggested that the use of the AHP method can facilitate in the collection and interpretation of local ecological knowledge by scientists. Moreover, the output of this procedure, the vector of weights, can be used for comparison with scientific data collected by traditional means and for comparison with the observations of local peoples from other geographical locations.

Applications of Low Altitude Remote Sensing in Agriculture upon Farmers' Requests- A Case Study in Northeastern Ontario, Canada

With the growth of the low altitude remote sensing (LARS) industry in recent years, their practical application in precision agriculture seems all the more possible. However, only a few scientists have reported using LARS to monitor crop conditions. Moreover, there have been concerns regarding the feasibility of such systems for producers given the issues related to the post-processing of images, technical expertise, and timely delivery of information. The purpose of this study is to showcase actual requests by farmers to monitor crop conditions in their fields using an unmanned aerial vehicle (UAV). Working in collaboration with farmers in northeastern Ontario, we use optical and near-infrared imagery to monitor fertilizer trials, conduct crop scouting and map field tile drainage. We demonstrate that LARS imagery has many practical applications. However, several obstacles remain, including the costs associated with both the LARS system and the image processing software, the extent of professional training required to operate the LARS and to process the imagery, and the influence from local weather conditions (e.g. clouds, wind) on image acquisition all need to be considered. Consequently, at present a feasible solution for producers might be the use of LARS service provided by private consultants or in collaboration with LARS scientific research teams.

The Use of Multipolarized Spaceborne SAR Backscatter for Monitoring the Health of a Degraded Mangrove Forest

Abstract To determine whether multipolarized spaceborne synthetic aperture radar could be used to monitor the health of a mangrove forest, leaf area index, as well as other biophysical parameter data, from stands dominated by white mangrove (Laguncularia racemosa) and located within a degraded mangrove forest were examined in relation to backscatter coefficients from ENVISAT synthetic aperture radar scenes. The results indicate that polarization and, to a lesser extent, incident angle play a significant role in the ability to estimate both leaf area index and mean tree height. No significant linear coefficients of determination were observed between the recorded parameters and the backscatter coefficient from any of the copolarized scenes. With regards to leaf area index, r2 values of 0.82 and 0.73 were calculated for the cross-polarized data at two incident angles. For mean tree height, the linear coefficient of determination was much higher for the smaller incident angle data than for the larger incident angle data. No significant relationships were identified for stem density, basal area, or mean diameter at breast height. It is postulated that the inability of the copolarized ENVISAT advanced synthetic aperture radar data to differentiate between dead mangrove stands and healthy ones is the result of equally high backscatter resulting from strong scattering from trunk–ground double bounce and crown volume, respectively.

An object-oriented classification method for mapping mangroves in Guinea, West Africa, using multipolarized ALOS PALSAR L-band data

The principal objective of this study was to determine the accuracy of an object-based image analysis (OBIA) approach in classifying mangroves from spaceborne synthetic aperture radar (SAR) data, specifically Advanced Land Observation Satellite (ALOS), phased array L-band synthetic aperture radar (PALSAR), and single-polarized (HH) and dual-polarized (HH + HV) L-bands. The accuracy of the object parameters was examined to determine the optimal colour and shape ratios for the hierarchical classification. At the first level of classification (mangroves from non-mangroves), the results indicate that it is possible to accurately separate mangrove areas from saltpan and water/shallow zones using both sets of SAR images for the Mabala and Yélitono islands of southern Guinea. The final accuracies, based on the most optimal object parameters, were 91.1% and 92.3% for the single- and dual-polarized data, respectively. At the second level of classification, separation among the three mangrove classes identified was most accurate when using the dual-polarized data, at an overall accuracy of only 63.4%. The three mangrove classes identified included tall red mangrove (Rhizophora racemosa), dwarf red mangrove (R. mangle and R. harisonii), and black mangrove (Avicennia germinans). Using the optimal combination of parameters, the extent to which a filter could be used to improve the accuracy was examined. At this level, it was determined that the dual-polarized data, filtered with a 3 × 3 Lee speckle filter and a segmentation scale of 5, resulted in an overall accuracy of 64.9%. Consequently, it is recommended that for persistently cloud-covered regions, such as Guinea, ALOS PALSAR data using an OBIA could be useful as a quick method for mapping and monitoring mangroves.

Spectral response to varying levels of leaf pigments collected from a degraded mangrove forest

Mangrove forests are being removed or degraded at an alarming rate, even though they play a vital role in the sustainability of tropical coastal communities. Many of these forests are identified as degraded based on observable changes in their leaves (e.g., density, size, color, etc.). Of these, color can be considered one of the most important indicators of degradation because changes in the spectral response may be indicative of changes in the leaf pigment content. In this investigation, hyperspectral laboratory techniques were applied to examine potential relationships between the mangrove leaf spectral response and three leaf pigments: chlorophyll a, chlorophyll b, and total carotenoid content. Using an ASD spectroradiometer, the spectral reflectance of leaf samples were collected from poor condition, dwarf and healthy black (Avicennia germinans) and from healthy and poor condition red (Rhizophora mangle) mangroves located in a degraded mangrove system of the Mexican Pacific. A subset of 150 representational leaves was then used for pigment content analysis. The results indicate significant relationships between the spectral response and the levels of chlorophyll a, b, and total carotenoid content contained in the leaves. In particular, wavebands at the red edge position were shown to be the best predictors of the pigment contents. The results also indicate that vegetation indices do not necessarily improve the ability to predict these constituents. Finally, the red edge position was found to be significantly different between the healthy and poor condition mangroves ( P = 0 ), with the healthy mangroves having longer wavelengths associated with the red edge position.