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Formatting Array Input Data File in RES2DINV: surface electrodes for any geometry

pseudosection for 2D resistivity surveys

Example of electrodes arrangement and measurement sequence that can be used for a 2-D electrical imaging survey is shown on the left. Many different multi-electrode systems have been developed over the past 15 years using different arrangements of the cables and measurement strategies (Loke, 2011). This program is designed to invert large data sets (with about 200 to 100000 data points) collected with a system with a large number of electrodes (about 25 to 16000 electrodes). The survey is usually carried out with a system where the electrodes are arranged along a line with a constant spacing between adjacent electrodes. However, the program can also handle data sets with a non-uniform electrode spacing. RES2DINV program can be used for surveys using the Wenner, pole-pole, dipole-dipole, pole-dipole, Wenner-Schlumberger, gradient and equatorial dipole-dipole (rectangular) arrays. In addition to these common arrays, the program even supports non-conventional arrays with an almost unlimited number of possible electrode configurations (Loke et al. 2010). You can process pseudo sections with up to 16000 electrode positions and 70000 data points at a single time on a computer with 4 gigabytes (GB) of RAM. Besides normal surveys carried out with the electrodes on the ground surface, the program also supports aquatic and cross-borehole surveys.

Locations

Los Angelos 34° 3' 8.0424" N, 118° 14' 37.266" W
5° 49' 22.6488" S, 34° 58' 49.6884" E

Extracting Geographical Lat-Long data from Google Earth KML / KMZ files to Excel

If you have some data in table format with IDs for fields or point locations on the map and Google Earth KML file with those fields having same IDs, it is generally possible to bring spatial information to Excel and merge those data sources together to use in further spatial analysis in other GIS software and in newly released FREE ESRI Maps for MS Office Beta 2. There are a few little tricks to it, though…

Google Earth KML files are essentially XML files with geographical information, but Excel will not open them directly.

image

Adding Lat-Long for the centroids of USA counties in a new point shapefile (ArcMap 10)

Software: ArcGIS - ArcEditor 9.2, 9.3, 9.3.1, 10 ArcGIS - ArcInfo 9.2, 9.3, 9.3.1, 10 ArcGIS - ArcView 9.2, 9.3, 9.3.1, 10 ArcGIS for Desktop Advanced 10.1 ArcGIS for Desktop Standard 10.1

USA counties center pointsThis is documented step-by-step and hands-on exercise on how to create XY point shapefile for the centers of USA counties (with linked basic demography and FIPS) in ArcMap 10.1. You don’t need to follow those steps (and if you don’t have ArcGIS for Desktop, you cannot) and may just grab the resulted layer file in various formats at the end of this post. Formats available are MS Excel table, CSV table with XY, zipped SHP file package, and KMZ file.

This layer is not directly shareable on ArcGIS Online, as it has more than 1000 features (3143, to be exact), we may post it there later as partial files…

If you need help with your GIS project, please, do not hesitate to contact Landviser, LLC - post comment, email info@landviser.com, or call 609-412-0555. Current complete catalog of Landviser LLC

Quick Estimation of Salinity in Field Soils and Irrigation Water with LandMapper ERM-02

ec mapping with Landmapper on dead rice field after hurracaine IkeSoil salinity is routinely evaluated in the labs from electrical conductivity of liquid soil saturation extract (ECe). The resulted total salinity is reported either directly in conductivity units (dS/m) or converted to TDS (total dissolved solids) concentration in ppm (parts per million) using formula: 1 dS/m = 1 mS/cm = 1 mmho/cm = 640 ppm = 640 mg/L= 0.64 g/L=0.064%

But now EC of soil and waters can be measured directly in the field using highly accurate method of four-electrode probe and Landmapper ERM-02 measuring device. Best of all, probes can be build to sense different soil layers down to 30 ft! Probes are simple and inexpensive to make from common materials available at any hardware store.

For irrigation water and soil solutions: To measure ECw just put 4-electrode probe of Landmapper used for mapping into a ditch, canal, or other water source. Make sure that all 4-electrodes are in contact with water. Take a reading in EC (conductivity) mode. Display will read (example):  
K0*C= 150m  - which indicates milli Siemens (mS/m)
To convert to dS/m, divide display number by 100, i.e. 150 mS/m=1.5 dS/m.

Vertical Electrical Sounding to detect peat deposit thickness and drying depth

VES to detect peat deposit depthThe valley landscapes of humid areas are dominated with peat soils of various origins, which become the most productive soils after the proper drainage and cultivation. The high fertility and proximity to water make peat soils the most desirable for vegetable production. However, these soils are also subject to quick degradation during agricultural usage. Excess drainage increases the unproductive decomposition and mineralization of peat and can cause spontaneous ignition of peat soils, whereas little or no drainage can be non-sufficient for normal agricultural practices. Therefore, drainage design and the following agriculture practice on peat soils should be based on careful studies of the peat soil genesis and hydrology of the areas.

 Method VES is suitable for detection the resistivity in different soil and geological strata without digging or boring. Usually, peat shows not much difference in electrical properties along the profile. Water content of cultivated peat soils is close to the field capacity during the whole growing season.

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Electrical geophysical methods to outline ground water rising in urban areas

Hydrological conditions in Delta Volga, RussiaThe groundwater table rises steadily in the delta Volga, where Astrakhan’ city is located because of irrigation and rising of the Caspian Sea level. The highly saline groundwater enhances secondary salinity in the area. The groundwater caused visible destruction of more than 20% of the buildings in Astrakhan’ city. Natural hazardous groundwater condition in delta Volga was further aggravated in the urban areas by the uncontrolled leakage from the canals and plumbing pipes.

The methods of vertical electrical sounding (VES) and non-contact electromagnetic profiling (NEP) were tested in 1995 for detail outlining of the groundwater table within the representative part of Astrakhan’ city. The study area was located in the center of Astrakhan’ with a large change of elevation, which induced a high variation of groundwater table within the area.map of geophysical survey in Astrakhan City

Profiles of alluvial soils in delta Volga consist of thin layers of silt, clay, and sand. However, only water and salt content distributions within the soil profile cause considerable differentiation of the electrical resistivity in these soils. The soil profile can be generally divided into the top unsaturated layer with high resistivity and the bottom layer saturated by saline groundwater with low resistivity. Considering high distinction in electrical resistivity between unsaturated and saturated zones, the VES method was applied for detection of groundwater table. With the 1-D computer interpretation of the VES data the transition between top layer with high resistivity and bottom layer with low resistivity (i.e. groundwater table) was determined accurately. Compared with the groundwater tables measured in wells, the relative errors of the VES estimation were from 3 to 13%.

Electrical resistivity in precision cranberry farming

Low ER indicates low cranberry yieldOne of the most important issues in precision agriculture is to develop site specific principles of crop management based on variability of soil and hydrological properties. Accessing spatial variability of soil properties often require high-density and repetitious sampling, which is costly, time-consuming, and labor-intensive. One of the challenges facing the adoption of precision agriculture technology is the identification of productivity-related variability of soil properties accurately and cost-effectively.

The application of the geophysical methods of electrical resistivity makes it possible to define areas of electrically contrasting soils, which have distinct properties and, therefore, should be used in agriculture in different ways. Electrical resistivity is a composite characteristic of soils, which generally related to soil texture, stone, salt, and humus contents, and arrangement of the genetic soil horizons. This is the complex of the factors, which directly influence yield of the most of the crops. The advantage of measuring electrical resistivity is that it can be measured directly in the field without actual taking of soil samples and analyzing them in the laboratory. Thus, implication of the electrical resistivity techniques of soil characterization can tremendously decreases time and labor, required to delineate management zones within the fields.

Locations

Chatsworth, NJ 39° 49' 3" N, 74° 32' 7.0008" W
Puerto Varas 41° 19' 58.6704" S, 72° 58' 55.8408" W

Vertical Electrical Sounding to Detect Groundwater Levels in Arid Areas

hydrology of delta Volga, RussiaWater and salt content distributions within the soil profile are the main properties causing considerable variations in electrical resistivity. In arid areas, the water content and salt distributions are determined mainly  by the saline groundwater, rather then by precipitation. 

 

The soil profile is divided into a top unsaturated layer with high resistivity and a bottom layer saturated by saline groundwater with low resistivity. Considering large differences in electrical resistivity between the unsaturated and saturated zones, the VES method was applied to detect the saline groundwater level. 

Location

Gandurino, AST 45° 50' 56.4" N, 48° 0' 23.04" E

Vertical Electrical Sounding to Detect Soil Salinity in Arid Areas

total soil salinity vs resistivity by VESWater and salt content distributions within the soil profile are the main properties causing considerable variations in electrical resistivity or conductivity.  Since the evaporation in the arid areas (Astrakhan, Russia) is about five times higher than the precipitation, the water content and salt distributions are determined mainly by the saline groundwater.

The differentiation of salinity in the unsaturated zone of the soil profiles was revealed by small fluctuations of electrical resistivity in upper part of the VES profiles. We thoroughly interpreted the VES results to estimate the layers with different electrical conductivities (EC) for 12 soil profiles. The total salt content was measured in soil samples collected from the layers of the profiles as shown in Table (columns 1 and 2) for one example profile. 

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