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United States Department of Agriculture

Agricultural Research Service

Research Project: A LASER SYSTEM FOR HIGH-RESOLUTION SOIL SURFACE AND STANDING RESIDUE ANALYSIS

Location: Engineering and Wind Erosion Research Unit

2012 Annual Report


1a.Objectives (from AD-416):
The overall objective of this cooperative research project is to: develop a real-time, field portable, measurement system that is capable of measuring geo-referenced surface elevations and standing residue with sub-centimeter accuracy for both elevation measurement and geo-referencing. Specific objectives are: .
1) develop the hardware and software for a system that integrates a precision laser distance meter, a gyroscope and an RTK GPS with a portable computer; .
2)develop a mounting frame and linear rail on a vehicle that supports the laser system and controls the translation movement of the laser; .
3)conduct field tests to evaluate the system for measuring roughness of soil surface with and without crop residue and live vegetative cover; .
4)conduct field tests to evaluate the system’s ability to measure micro-relief of riparian buffer zones; and.
5)conduct field tests to evaluate the device’s ability to describe standing residue coverage, both height and areal distributions.


1b.Approach (from AD-416):
The approach is to develop this system with five major components: .
1)a distance-measuring unit,.
2)a frame and rail unit,.
3)a frame angular-position measuring unit,.
4)a geo-referencing unit, and.
5)a data-acquisition and control unit. Functions of these components are:

1. Distance-measuring unit - This unit measures the vertical distance between soil surface and the frame, on which the laser sensor is mounted. An “Acquity” sensor, which uses a fixed infrared laser and a rotating mirror to scan the soil surface along a straight line, will be used for distance measurement. In addition to distance measurement, this sensor also provides information on reflected light intensity. Thus, it is possible to distinguish between the top of canopies and actual soil surface using signal processing if soil surface is not completely covered by the canopy.

2. Frame and rail unit - Since the laser sensor only measures elevations along a straight line, a rail is needed to move the sensor in the direction perpendicular to the scan line so that elevations within a rectangular area can be measured. The rail will be supported by a frame. The sensor will travel along the rail, driven by a linear actuator; and the position of the sensor, monitored using an optical encoder, will be used as a feedback control signal to accurately control the sensor position. Several other devices, including a gyroscope to measure the angular position of the frame and an RTK GPS unit, will also be mounted on the frame.

3. Frame angular-position measuring unit - Because the laser-distance sensor will be mounted on the frame, angular displacements of the frame become critical to the accuracy of elevation measurement. Angular displacements of the frame - pitch, roll, and yaw - will be measured using a rate-integrating gyroscope. X, Y, Z coordinates of the laser scan lines on the soil surface will then be corrected using these measured angles.

4. Geo-reference unit -A Real-time Kinematic (RTK) GPS will be used to help register the measured surface points into a geographic coordinate system (UTM, Lat-lon, or a local coordinate system). An RTK GPS unit is needed because this is the only GPS device that provides a sub-centimeter accuracy in longitude and latitude.

5. Data-acquisition and control unit –All control and data signals from the laser, gyroscope, optical encoders and RTK GPS unit will be processed using a laptop computer.


3.Progress Report:

A laser system was constructed to: a) improve upon surface roughness measurements currently made with a line-transect pin meter; b) investigate the system’s ability to distinguish between flat residue on the surface and the soil; and c) to investigate the system’s ability to detect standing residue. The laser has been constructed as outlined above with the listed components. The system has undergone a recent rewiring of the components to make it more robust for field use and the software revised based upon experiences using the laser system collecting data in the field. This year’s tasks were to be performed to assess the feasibility of using the laser to distinguish between flat residue and the soil surface, with the ultimate goal of using it as a simple residue cover meter.

Laboratory experiments were to be conducted with the laser distance meter to determine the accuracy and feasibility of measuring flat residue (wheat straw, corn stover, milo stalks, soybean residue, etc.) on a variety of soil surfaces under different moisture conditions. Initial preliminary data were collected for comparison purposes using the laser system, a high resolution digital camera and a Sony camcorder with the infrared “nightshot” feature enabled. All three systems had issues distinguishing some of the residue on the surface from the soil. The residue being evaluated was decayed corn stalks. The Sony camcorder performed the best in those preliminary studies. If this system eventually proves successful, it would dramatically speed up the time required to obtain residue cover data in the field.

Work was progressing on evaluating various filtering methods and how to best incorporate the “distance” information available from the laser to improve its accuracy in determining residue from the soil surface. However, the graduate student working on the project left the BAE program before this could be fully evaluated.


Last Modified: 4/15/2014
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