Radar level gauge

1. A radar level gauge for determining a distance to a surface of a product in a tank, said radar level gauge comprising:

a transceiver configured to transmit an electromagnetic transmit signal with varying frequency towards said surface and to receive an electromagnetic return signal, via a signal propagation device;

a mixer adapted to mix the transmitted electromagnetic transmit signal with the received electromagnetic return signal to provide a mixer output signal including information about the surface's echo and information about another echo; and

processing circuitry configured to apply an algorithm to the mixer output signal, which algorithm provides a distance-level rate matrix wherein the surface's echo and said another echo each is determined in two dimensions, wherein the two dimensions are distance and level rate, and to determine the distance to the surface based on the thus determined echo of the surface.

2. A radar level gauge according to claim 1 , wherein said surface is moving, wherein said another echo comes from an element in or of said tank, which element is stationary or moving at a different level rate than the moving surface, and wherein the processing circuitry in applying the algorithm is configured to resolve the moving surface's echo and said element's echo.

3. A radar level gauge according to claim 2 , wherein said element is a disturbance in said tank, and wherein the processing circuitry in applying the algorithm is configured to resolve the moving surface's echo and the disturbance's echo while the moving surface passes the disturbance in said tank.

4. A radar level gauge according to claim 2 , wherein said element is the bottom of said tank.

5. A radar level gauge according to claim 1 , wherein the electromagnetic transmit signal comprises a plurality of frequency sweeps.

6. A radar level gauge according to claim 5 , wherein there is a delay after each frequency sweep of said plurality of frequency sweeps.

7. A radar level gauge according to claim 5 , wherein the processing circuitry is configured to apply the algorithm to the mixer output signal by:

performing a first Fast Fourier Transform on the mixer output signal for each of at least some frequency sweeps of the plurality of frequency sweeps of the electromagnetic transmit signal;

storing the resulting spectra in a distance-time matrix; and

performing a second Fast Fourier Transform for each distance in the distance-time matrix giving the distance-level rate matrix in which the surface's echo and said another echo each is determined in the two dimensions.

8. A radar level gauge according to claim 1 , wherein the algorithm is a range Doppler algorithm.

9. A radar level gauge according to claim 1 , wherein the radar level gauge is a Frequency Modulated Continuous Wave radar level gauge.

10. A method of determining a distance to a surface of a product in a tank, which method comprises:

transmitting an electromagnetic transmit signal with varying frequency towards said surface;

receiving an electromagnetic return signal;

mixing the transmitted electromagnetic transmit signal with the received electromagnetic return signal to provide an output signal including information about the surface's echo and information about another echo;

applying an algorithm to the output signal, which algorithm provides a distance-level rate matrix wherein the surface's echo and said another echo each is determined in two dimensions, wherein the two dimensions are distance and level rate; and

determining the distance to the surface based on the thus determined echo of the surface.

11. A method according to claim 10 , wherein said surface is moving, wherein said another echo comes from an element in or of said tank, which element is stationary or moving at a different level rate than the moving surface, and wherein applying the algorithm includes resolving the moving surface's echo and said element's echo.

12. A method according to claim 11 , wherein said element is a disturbance in said tank, and wherein applying the algorithm includes resolving the moving surface's echo and the disturbance's echo while the moving surface passes the disturbance in said tank.

13. A method according to claim 11 , wherein said element is the bottom of said tank.

14. A method according to claim 10 , wherein the electromagnetic transmit signal comprises a plurality of frequency sweeps.

15. A method according to claim 14 , wherein there is a delay after each frequency sweep of said plurality of frequency sweeps.

16. A method according to claim 14 , wherein applying the algorithm to the output signal comprises:

performing a first Fast Fourier Transform on the output signal for each of at least some frequency sweeps of the plurality of frequency sweeps of the electromagnetic transmit signal;

storing the resulting spectra in a distance-time matrix; and

performing a second Fast Fourier Transform for each distance in the distance-time matrix giving the distance-level rate matrix in which the surface's echo and said another echo each is determined in the two dimensions.

17. A method according to claim 10 , wherein the algorithm is a range Doppler algorithm.

18. A non-transitory computer program product comprising computer program code to perform, when executed on a computer, the steps of:

applying an algorithm to an output signal, which output signal is provided by mixing an electromagnetic transmit signal transmitted towards a surface of a product in a tank with a received electromagnetic return signal, wherein the output signal includes information about the surface's echo and information about another echo, wherein the algorithm provides a distance-level rate matrix wherein the surface's echo and said another echo each is determined in two dimensions, wherein the two dimensions are distance and level rate; and

determining the distance to the surface based on the thus determined echo of the surface.