A LASER SYSTEM FOR HIGH-RESOLUTION SOIL SURFACE AND STANDING RESIDUE ANALYSIS
Location: Engineering and Wind Erosion Research Unit
Project Number: 5430-11120-009-03
Specific Cooperative Agreement
Start Date: May 01, 2008
End Date: Apr 30, 2013
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.
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.