Andreas Persson

Comparison of DEM Data Capture and Topographic Wetness Indices

Digital elevation models (DEMs) can be captured and analysed by various methods. Elevation capturing with RTK-GPS and airborne laser scanning is presented and evaluated in terms of height accuracy of raw data and interpolated DEMs for study sites in Sweden and Germany. Applications for precision agriculture are based on the connection of land surface and the movement of water in the landscape. Three methods of deriving potential flow accumulation from DEMs are discussed. Results indicate that the Topographic Wetness Index can be used to assess the pattern of potential soil moisture on a field and changes in soil texture caused by erosion processes. The quality of the soil moisture assessment varies with both flow algorithm and terrain characteristics. Correlations up to r2 = 0.64 were found. Best results were obtained on undulating farmland using the DEMON algorithm and a formbased approach. However, in areas with low relief, the concept did not lead to valuable soil moisture maps.

Influence of the permafrost boundary on dissolved organic matter characteristics in rivers within the Boreal and Taiga plains of western Canada

Catchment export of terrestrial dissolved organic matter (DOM) and its downstream degradation in aquatic ecosystems are important components of landscape scale carbon balances. In order to assess the influence of peatland permafrost on river DOM characteristics, we sampled 65 rivers along a 900 km transect crossing into the southern discontinuous permafrost zone on the Boreal and Tundra Plains of western Canada. Catchment peatland cover and catchment location north or south of the permafrost boundary were found together to have strong influences on dissolved organic carbon (DOC) concentrations and DOM chemical composition. River DOC concentrations increased with catchment peatland cover, but were consistently lower for catchments north of the permafrost boundary. In contrast, protein fluorescence (PARAFAC analysis), was unrelated to catchment peatland cover but increased significantly in rivers north of the permafrost boundary. Humic and fulvic acid contribution to DOM fluorescence was lower in rivers draining catchments with large lakes than in other rivers, consistent with extensive photodegradation, but humic and fulvic acid fluorescence were also lower in rivers north of the permafrost boundary than in rivers to the south. We hypothesize that shifts in river DOM characteristics when crossing the permafrost boundary are related to the influence of permafrost on peatland hydrological connectivity to stream networks, peatland DOM characteristics and differences in DOM degradation within aquatic ecosystems.

Spatial Influence of Topographical Factors on Yield of Potato ( Solanum Tuberosum L.) in Central Sweden

This study has evaluated the sampling density for creation of high-resolution digital elevation models (DEMs) for precision agriculture purposes. The relationships between yield and topographical factors were investigated in a study area located in the central Sweden province of Dalarna. The DEM data sampling was carried out with a RTK-GPS system. A dense sampling scheme was employed and data was divided into two for both interpolation and validation. Kriging interpolation was used for DEM generation. From the DEM, topographical parameters were extracted and topographical indices were estimated. The indices were calculated with slope length and its vertical and horizontal components. The drainage area for a point of interest and the relationship of this area to the total drainage area were also estimated. The relationship of yield and the topographical parameters and indices was investigated using both circular and spatial statistics. A spatial regression was used to calculate a model for the relationship. Up to 20% of the yield could be explained in the final model for one of the fields.

High Resolution Mapping of Peatland Hydroperiod at a High-Latitude Swedish Mire

Monitoring high latitude wetlands is required to understand feedbacks between terrestrial carbon pools and climate change. Hydrological variability is a key factor driving biogeochemical processes in these ecosystems and effective assessment tools are critical for accurate characterization of surface hydrology, soil moisture, and water table fluctuations. Operational satellite platforms provide opportunities to systematically monitor hydrological variability in high latitude wetlands. The objective of this research application was to integrate high temporal frequency Synthetic Aperture Radar (SAR) and high spatial resolution Light Detection and Ranging (LiDAR) observations to assess hydroperiod at a mire in northern Sweden. Geostatistical and polarimetric (PLR) techniques were applied to determine spatial structure of the wetland and imagery at respective scales (0.5 m to 25 m). Variogram, spatial regression, and decomposition approaches characterized the sensitivity of the two platforms (SAR and LiDAR) to wetland hydrogeomorphology, scattering mechanisms, and data interrelationships. A Classification and Regression Tree (CART), based on random forest, fused multi-mode (fine-beam single, dual, quad pol) Phased Array L-band Synthetic Aperture Radar (PALSAR) and LiDAR-derived elevation to effectively map hydroperiod attributes at the Swedish mire across an aggregated warm season (May-September, 2006-2010). Image derived estimates of water and peat moisture were sensitive (R-2 = 0.86) to field measurements of water table depth (cm). Peat areas that are underlain by permafrost were observed as areas with fluctuating soil moisture and water table changes.

On generating digital elevation models from liDAR data – resolution versus accuracy and topographic wetness index indices in northern peatlands

Abstract Global change and GHG emission modelling are dependent on accurate wetness estimations for predictions of e.g. methane emissions. This study aims to quantify how the slope, drainage area and the TWI vary with the resolution of DEMs for a flat peatland area. Six DEMs with spatial resolutions from 0.5 to 90 m were interpolated with four different search radiuses. The relationship between accuracy of the DEM and the slope was tested. The LiDAR elevation data was divided into two data sets. The number of data points facilitated an evaluation dataset with data points not more than 10 mm away from the cell centre points in the interpolation dataset. The DEM was evaluated using a quantile-quantile test and the normalized median absolute deviation. It showed independence of the resolution when using the same search radius. The accuracy of the estimated elevation for different slopes was tested using the 0.5 meter DEM and it showed a higher deviation from evaluation data for steep areas. The slope estimat...

EVALUATION OF AN OPTICAL SENSOR FOR TUBER YIELD MONITORING

A sensor for monitoring the yield of tubers was tested in the laboratory and in the field. The laboratory test was designed to investigate whether the sensor varied in its measurements of tuber size, whether the recorded size differed within the width of the sensor, and whether tilting of the sensor affected the result. The test objects were spheres, and measurements were carried out on three different sizes. A statistical analysis showed how the sensor measured the sizes for the different combinations of size, position, and inclination. In the field, a harvester-mounted sensor was used to monitor yield of Bintje potatoes in terms of tuber size and weight. The results obtained were compared with those from mechanical load-cell measurements. An expression relating tuber size to weight was determined. Plot-harvesting tubers provided data for evaluation of tuber size in relation to yield. The results showed that the errors in size determination by the sensor were in the order of 1% to 2%. Different size classes were well differentiated. Some differences were noted for object position and sensor inclination. Field tests showed that the mean deviation from measured weight was about 1%. It was concluded that sensor errors were small and that the sensor could discriminate between different sizes for the spheres used in the study. In the field, the sensor worked with good consistency and is a potential option for tuber yield monitoring.

Cropland changes in times of conflict, reconstruction, and economic development in Iraqi Kurdistan

The destruction of land and forced migration during the Anfal attacks against the Kurds in Iraq in the late 1980s has been reported to have severe consequences for agricultural development. A reconstruction program to aid people in returning to their lands was launched in 1991. To assess the agricultural situation in the Duhok governorate during the pre-Anfal (A), post-Anfal (B), reconstruction (C), and present (D) periods, we mapped winter crops by focusing on inter-annual variability in vegetation greenness, using satellite images. The results indicate a decrease in cultivated area between period A and B, and a small increase between period B and C. This supports reports of a decline in cultivated area related to the Anfal campaign, and indicates increased activity during the reconstruction program. Period D showed a potential recovery with a cropland area similar to period A.

Is the subarctic landscape still a carbon sink? Evidence from a detailed catchment balance

Climate warming raises the question whether high-latitude landscape still function as net carbon (C) sinks. By compiling an integrated C balance for an intensely studied subarctic catchment, we sho ...

Modelling flow routing in permafrost landscapes with TWI : an evaluation against site-specific wetness measurements

In northern peatlands the thawing of permafrost increasing the active layer depth and changing the hydrology may lead to feedbacks in the climate system through changes in the biogeochemistry of carbon. We are examining this association on the Stordalen peatland complex in subarctic Sweden by analyzing a DEM derived from LiDAR-data and the calculated TWI. The DEM, with a spatial resolution of 1 m, and the TWI are evaluated against two seasons of water level measurements from 30 sites in the peatland. The TWI is calculated with a form-based flow routing algorithm which produces a natural flow routing pattern. In permafrost wetlands the topography is the major driver and is very important even though its magnitude is low. Site-specific wetness (SSW) measurements from the sites were compared with the different peatland types that occur in the study area, i.e. fen, internal fen and palsa. The results showed a strong correlation between the TWI and the palsa. The TWI was better at describing general patterns than site-specific hydrology. The evaluation of spatial patterns of TWI against SSW reveal the resolution required to develop the technique to be useful for climate change studies.

Estimating slope from raster data – a test of eight algorithms at different resolutions in flat and steep terrain

Abstract Different slope algorithms can result in totally different estimates. In the worst case, this may lead to inappropriate and useless modelling estimates. A frequent lack of awareness when choosing algorithms justifies a thorough comparison of their characteristics, making it possible for researchers to select an algorithm which is optimal for their purpose. In this study, eight frequently used slope algorithms applied to Digital Elevation Models (DEMs) are compared. The influences of the resolution of the DEM (0.5, 1, 2, and 5 metres), as well as the terrain form (flat and steep terrain), are considered. It should be noted that the focus of the study is not to compare estimates with ‘ground truth’ data, but on the comparisons between the algorithms, and the ways in which they might differ depending on resolution and terrain. Descriptive statistics are calculated in order to characterize the general characteristics of the eight tested algorithms. Eight combinations of DEM resolution and terrain for...