Abstract: Applicants' ATR system is weather-agile because it is comprised of a primary target sensing means that is capable of surveilling the target scene in foul or fair weather, and a secondary target sensing means that is also capable of sensing targets in various weather. The primary and secondary sensing means communicate through a control center so that ultimately, among several weapons available, the most strategically located and equipped weapon is activated for the destruction of a selected target, given the weather. The control center accomplishes the communication by receiving the sensed target signature from the primary sensing means, processing the signature using database already resident in the center and transmitting the processed target signature to the weapon possessing the greatest potential for successfully destroying the target.

Abstract: An apparatus for identifying a buried object using ground penetrating radar (GPR) in a system containing at least one GPR sensor, comprises a data processor for detecting spatial correlations in data received from a GPR sensor in the apparatus and an image processor capable of building a data structure corresponding to an image of the buried object from data processed by the data processor. A method for identifying a buried object using GPR in a system containing a GPR sensor comprising detecting spatial correlations in data received from the GPR sensor in the system and building a data structure corresponding to an image of the buried object from the received data.

Abstract: The invention concerns a passive radar receiver with an array of antennas for a OFDM received signal comprising frames of symbols each emitted on coded orthogonal carriers. After formatting received signals into digital symbols, dummy signals from dummy OFDM emitters at different distances from and in different directions relative to the receiver are generated and added to the signals picked up by the antennas. The modified received signals are filtered by means of inverse covariance matrices in order to eliminate at least unwanted zero Doppler effect signals and to provide an isotropic reception diagram without blind sector of direct path being generated and by detecting mobile targets along the direct path.

Abstract: A mechanism for combining signals of multiple radars to achieve increased range, radar sensitivity and angle accuracy is provided. A first signal beam is radiated from an antenna of a first radar in the direction of a target. A second signal beam is radiated from an antenna of a second radar in the direction of the same target. The echo signals from the first signal beam and the second signal beam are received at both radars. The echo signals received at the first radar are processed to produce first radar processed echo signals and the echoes signals received at the second radar are processed to produce second radar processed echo signals. The first and second radar processed echo signals are combined to form an aggregate value.

Abstract: The system and method for standoff detection of human carried explosives (HCE) is a portable system that automatically detects HCE up to a range of 200 meters and within seconds alerts an operator to HCE threats. The system has radar only, or both radar and video sensors, a multi-sensor processor, an operator console, handheld displays, and a wideband wireless communications link. The processor receives radar and video feeds and automatically tracks and detects all humans in the field of view. Track data continuously cues the narrow beam radar to a subject of interest, the radar repeatedly interrogating cued objects, producing a multi-polarity radar range profile for each interrogation event. Range profiles and associated features are automatically fused over time until sufficient evidence is accrued to support a threat/non-threat declaration hypothesis. Once a determination is made, the system alerts operators through a handheld display and mitigates the threat if desired.

Abstract: The direct path of a radio signal from the transmitter to the receiver is frequently interfered with by reflections of the transmitted signal from stationary and moving objects. These reflections are known as multipath noise. The multipath canceler of this invention takes as input the direct path signal plus multipath noise. The canceler, after canceling the multipath noise, outputs a purified version of the direct path signal nearly devoid of multipath noise. The output of the canceler is fed back to a bank of delayers and frequency shifters. The outputs of this bank of delayers and frequency shifters are multiplied by a set of adjustable coefficients. These coefficients are adjusted to form very accurate replicas of the multipath reflections caused by each reflector. Which replicas are subtracted from the input which is the original direct path signal plus the multipath noise.

Abstract: A GPS receiver receives GPS spread spectrum communication signals subject to carrier demodulation and code phase autocorrelation using tightly coupled Kalman filter residual estimation based on Ricatti matrix computation for generating code phase errors and carrier phase errors for improved code phase tracking and carrier phase tracking in feedback loops for use in navigation systems.

Abstract: A method for incorporating a forward ranging feature into a radar altimeter is described. The method comprises positioning an antenna of the altimeter such that a side lobe of a radar signal radiates from the antenna in a forward direction and processing a radar return from the side lobe to determine a range to a forward object.

Abstract: A method for calculating a center frequency and a bandwidth for a radar doppler filter is herein described. The center frequency and bandwidth are calculated to provide radar performance over varying terrain and aircraft altitude, pitch, and roll. The method includes receiving an antenna mounting angle, a slant range, and velocity vectors in body coordinates, calculating a range swath doppler velocity, a track and phase swath bandwidth, and a phase swath doppler velocity. The method continues by calculating a range swath center frequency based on the range swath doppler velocity, calculating a phase swath center frequency based on the phase swath doppler velocity, and calculating a level and verify swath bandwidth based upon the track and phase swath bandwidth.

Abstract: Methods and apparatus for detecting objects. In one embodiment, a person entering a secured or “Safe Zone™” is illuminated with low-power polarized radio waves. Differently polarized waves which are reflected back from the person are collected and measured. In a preferred embodiment, concealed weapons are detected by calculating the difference of a pair of differences (Delta A and B) of different polarized reflected energy (upper and lower curves in the two graphs) in the time domain, and by using signal processing methods and apparatus to improve the reliability of the detection process.

Abstract: A radar performs accurate and appropriate pairing even if peaks of approximately identical signal intensities or even if a plurality of peak groups having identical representative beam bearings exist in the frequency spectrum. First, the peak frequency of a peak which appears in the frequency spectrum is determined for each of an up-modulating interval and a down-modulating interval in predetermined beam bearings, and signal-intensity profiles in the beam bearings are extracted with regard to a plurality of beam portions which are adjacent to the beam bearings. Next, the correlation level between the signal-intensity profiles at the up-modulating interval and the down-modulating interval is determined, and pairing is performed in sequence starting from the profiles having a higher correlation level.

Abstract: The invention concerns a passive radar receiver with an array of antennas for a OFDM received signal comprising frames of symbols each emitted on coded orthogonal carriers. After formatting received signals into digital symbols, dummy signals from dummy OFDM emitters at different distances from and in different directions relative to the receiver are generated and added to the signals picked up by the antennas. The modified received signals are filtered by means of inverse covariance matrices in order to eliminate at least unwanted zero Doppler effect signals and to provide an isotropic reception diagram without blind sector of direct path being generated and by detecting mobile targets along the direct path.

Abstract: Combining signals includes receiving first signals having a first frequency and second signals having a second frequency. A first weight reflecting a signal-to-noise ratio associated with a first signal is determined for each first signal, and a first signal output is generate from the first signals in accordance with the first weights. A second weight reflecting a signal-to-noise ratio associated with a second signal is determined for each second signal, and a second signal output is generate from the second signals in accordance with the second weights. The first signal output and the second signal output are combined to yield a combined signal output.

Abstract: This invention features an improved technique for search and track surveillance. In this invention, distinct and random (in both space and time) signal beams are simultaneous transmitted from an array of transmitter source elements in a manner to cover all sectors about a source location. In addition, countermeasures against a system according to the invention are difficult because the signal waveforms for each beam are distinct and random, making prediction of any signal waveform for any beam very unlikely. An array of receiver sensor elements is provided to receive signals that are scattered from remote objects and may or may not be co-located with and share the elements of the source array element. The scattered signals are received and processed to yield the direction and range of the remote objects.

Abstract: A method for incorporating a forward ranging feature into a radar altimeter is described. The method comprises positioning an antenna of the altimeter such that a side lobe of a radar signal radiates from the antenna in a forward direction and processing a radar return from the side lobe to determine a range to a forward object.

Abstract: A radar device is described having means (12) for generating a first code, means (18) for modulating a transmission signal in a transmitting branch using the first code, means (32) for delaying the first code, means (20) for modulating a signal in a receiving branch using the delayed first code, and means for mixing a reference signal with a reception signal, multiple receiving channels (111, 112, . . . 11k) being provided, the receiving channels (111, 112, . . . 11k) having means (1201, 1202, . . . 120k) for generating additional codes (C1, C2, . . . Ck), the receiving channels (111, 112, . . . 11k) having means (131, 132, . . . 13k) for demodulating using the respective additional codes (C1, C2, . . . Ck), and means (15) being provided for modulating the transmission signal using at least one of the additional codes (C1, C2, . . . Ck). A method which may be implemented advantageously using the radar device described is also described.

Abstract: A ranging Doppler radar system for identifying, and measuring range, velocity, direction of movement of a vehicle with minimal interference from surrounding environs and with low probability of intercept by the vehicle. The transmitted radar signal is modulated with pseudorandom code which acts as a frequency spreading agent and which allows a radar system to resolve range to targets into discrete “range cells”. Range cells can be grouped to yield a “range segment” which defines a region of roadway, such as a school zone. Traffic can be monitored in all range cells, or only in a predetermined range segment. Maps of traffic flow and vehicle parameters are generated and displayed using radar output parameters. Images representing vehicles violating posted speed limits are identified and highlighted on the traffic flow maps.

Abstract: An uncorrelated clutter noise cancellation method and apparatus employing a measured ambiguity function sample for each randomly-modulated transmission pulse in a randomly-modulated pulsed Doppler radar system. The ambiguity function samples are calculated from a stored copy of the randomly-modulated transmission signal. Estimates of the uncorrelated clutter backscatter are first developed by calculating the amplitude and phase of the radar returns detected in target range and velocity cells corresponding to stationary scatterers. The stationary scatterer contribution to each target cell, computed according to the sample ambiguity function, is then subtracted to eliminate the uncorrelated noise component in the return signal for the target cell. This clutter cancellation technique does not rely on correlations between the randomly-modulated transmission signal and the clutter return signal.

Abstract: This invention features an improved technique for search and track surveillance. In this invention, distinct and random (in both space and time) signal beams are simultaneous transmitted from an array of transmitter source elements in a manner to cover all sectors about a source location. In addition, countermeasures against a system according to the invention are difficult because the signal waveforms for each beam are distinct and random, making prediction of any signal waveform for any beam very unlikely. An array of receiver sensor elements is provided to receive signals that are scattered from remote objects and may or may not be co-located with and share the elements of the source array element. The scattered signals are received and processed to yield the direction and range of the remote objects.

Abstract: A method of recognizing a radar target comprises producing a sequence of Doppler spectra of radar returns form a scene and producing therefrom a sequence of Doppler feature vectors for a target in the scene. Hidden Markov modelling (HMM) is then used to identify the sequence of Doppler feature vectors as indicating a member of a particular class of targets. HMM is used to identify the sequence of Doppler feature vectors by assigning to each feature vector an occurrence probability by selecting a probability distribution or state from a set thereof associated with a class of targets, multiplying the occurrence probabilities together to obtain an overall probability, repeating for other probability distributions in the set to determine a combination of probability distributions giving highest overall probability for that class of target, then repeating for at least one other class of targets and selecting the target class as being that which yields the highest overall occurrence probability.

Abstract: This invention relates to a spectral generator and a spectral generation method for receiving pre-processed range-doppler-sensor data and generating at least one noise-reduced high-resolution spectrum therefrom. The spectral generator comprises a window generator that generates a window which defines a plurality of range-doppler cells. The spectral generator further comprises a covariance matrix calculator that is in communication with the window generator to receive the range-doppler-sensor data within the window and calculate a covariance matrix estimate for a range-doppler cell of interest in the window. The spectral generator also includes a spectral calculator that is in communication with the covariance matrix calculator to calculate a high-resolution spectral vector based on a location matrix and a noise subspace matrix estimate.

Abstract: A radar system may include an antenna, a waveform generator for generating a plurality of waveforms for different polarizations and/or having different frequency components, and a transmitter connected to the waveform generator for transmitting the plurality of waveforms via the antenna. Moreover, the radar system may also include a receiver connected to the antenna for receiving reflected signals from targets, and a processor for iteratively deconvolving the reflected signals to generate target data. More particularly, the radar system and targets may be relatively movable with respect to one another, and the processor may therefore store reflected signals over a length of relative movement and generate the target data based upon the stored signals to thus provide a synthetic aperture radar (SAR) system or an inverse SAR (ISAR) system.

Abstract: The invention relates to a method of interference suppression in a radar system (10) and also to a system (10) operating according to the method. The system (10) incorporates a first antenna (40) and associated electronic circuits for emitting interrogating radar radiation towards a remote scene (S). Moreover, the system (10) also incorporates a second antenna (45) and associated electronic circuits for receiving interrogating radiation reflected from the scene (S) and generating correponding first and second processed signals. The first and second processed signals correspond to a broader main beam response of the antenna (45) and to a narrower main beam response thereof respectively. By mutually comparing the first and second processed signals, the system (10) is operable to identify those second processed signals affected by interference from the scene (S).

Abstract: First-arriving-pulse detector (FAP) circuitry includes a correlator circuitry and a threshold circuitry. The correlator circuitry correlates a received signal with a template signal to provide an output signal. The threshold circuitry provides a first-arriving-pulse signal depending on the relative values of the output signal of the correlator circuitry and a threshold signal.

Abstract: The present invention is directed to a system and method for Doppler track correlation for debris tracking in PCL radar applications. The disclosed embodiments describe the systems and methods used in the detection of debris pieces and the association of the Doppler signals from the debris pieces across multiple illumination channels. The present invention also provides computation of debris state vectors and the projection of trajectories to determine debris impact points.

Abstract: The invention concerns a passive radar receiver for a received orthogonal frequency division multiplex-type signal consisting of symbol frames each emitted on coded orthogonal carriers. After formatting the received signals into digital symbols (S1 S1), a filtering circuit (2) eliminates by subtraction or using a covariance matrix, in the symbol signal at least unwanted signals with null Doppler effect so as to apply a filtered signal (X′) including essentially signals backscattered by mobile targets to a Doppler-distance correlator (4).

Abstract: An apparatus and method of dynamically optimizing an acquisition range of a radar system, including modulating a CW radar signal with a PN code that has an adjustable code frequency of modulation and an adjustable chip length. The method includes transmitting the modulated radar signal and receiving a return radar signal, based on the transmitted radar signal. The method continuously measures a SNR of the received return radar signal, and adaptively tunes the adjustable code frequency of modulation, and adaptively tunes the adjustable chip length, based on the continuously measured SNR. In this manner, the acquisition range of the radar system is optimized.

Abstract: Correlating observations of objects in the sky to determine an orbit includes identifying an initially identified object, determining if the initially identified object will be identifiable again, and identifying a subsequently identified object. A determination is then made by comparing characteristics of the initially identified object with the subsequently identified object. If the object correlate to one another a path or orbit of the object can be determined using the characteristics of the initially identified object and the subsequently identified object.

Abstract: An apparatus for identifying a buried object using ground penetrating radar (GPR) in a system containing at least one GPR sensor, comprises a data processor for detecting spatial correlations in data received from a GPR sensor in the apparatus and an image processor capable of building a data structure corresponding to an image of the buried object from data processed by the data processor. A method for identifying a buried object using GPR in a system containing a GPR sensor comprising detecting spatial correlations in data received from the GPR sensor in the system and building a data structure corresponding to an image of the buried object from the received data.

Abstract: Combining signals includes receiving first signals having a first frequency and second signals having a second frequency. A first weight reflecting a signal-to-noise ratio associated with a first signal is determined for each first signal, and a first signal output is generate from the first signals in accordance with the first weights. A second weight reflecting a signal-to-noise ratio associated with a second signal is determined for each second signal, and a second signal output is generate from the second signals in accordance with the second weights. The first signal output and the second signal output are combined to yield a combined signal output.

Abstract: Correlating observations of objects in the sky to determine an orbit includes identifying an initially identified object, determining if the initially identified object will be identifiable again, and identifying a subsequently identified object. A determination is then made by comparing characteristics of the initially identified object with the subsequently identified object. If the object correlate to one another a path or orbit of the object can be determined using the characteristics of the initially identified object and the subsequently identified object.

Abstract: A system includes a storage medium storing contextual information about a target or target area, and a simulator communicatively coupled to the storage medium and operable to receive the contextual information. The simulator is operable to generate a set of simulated information about the target using the contextual information. The system further includes a sensor operable to collect a set of actual information about the target. A comparator is operable to generate a set of delta information in response to differences between the set of simulated information and the set of actual information. The delta information is transmitted and added to a second set of simulated information to generate a set of information that is substantially similar to the set of actual information.

Abstract: A method for processing radar return data to determine a physical angle, in aircraft body coordinates to a target, is disclosed. The radar return data includes a phase difference between radar return data received at an ambiguous radar channel and a left radar channel, a phase difference between radar return data received at a right radar channel and an ambiguous radar channel, and a phase difference between radar return data received at a right radar channel and a left radar channel. The method includes adjusting a phase bias for the three phase differences, resolving phase ambiguities between the three phase differences to provide a signal, and filtering the signal to provide a physical angle to the target in aircraft body coordinates.

Abstract: A method for resolving radar range ambiguities is disclosed, where the radar is modulated with a phase code which comprises a number of chips. The method includes acquiring a radar return within a verify gate, the verify gate being aligned with one chip of the phase code, determining an amplitude of the return, stepping the gate outbound to a next chip of the code, acquiring a return, and determining if the return has an amplitude greater than a threshold based on the original return. The verify gate is repeatedly stepped outbound to determine if a chip can be found which has an amplitude in excess of the threshold or until returns from all chips within the phase code have been acquired. If such a position is found, search logic of the radar is moved outbound to the chip position which had the highest amplitude return, if not the original chip position and the entire process begins again.

Abstract: A mixer used in a millimeter-wave band and a microwave band capable of achieving loss reduction, a radar module, and a communication apparatus incorporating the mixer and having high efficiency. The mixer includes two electrodes formed on one main surface of a dielectric substrate and another electrode formed on another main surface thereof such that non-electrode portions on both main surfaces are opposed to each other via the dielectric substrate. Additionally, a diode is connected bridging a slit between the two electrodes on one main surface to constitute a circuit board. The circuit board and a dielectric strip are arranged between upper and lower conductive plates.

Abstract: A complex signal correlator such as can be implemented in a correlation detector system affords a unique algorithm which estimates the codifference correlation between two complex signals based on the sum and difference of codifference estimates, each codifference estimate having equivalently associated therewith a dispersion estimate. Typical embodiments provide a receiving antenna and a receiver inclusive of the codifference correlator, wherein radio frequency waves are down converted and sampled, the sampled signals are correlated with a reference signal contained in a memory, and the resultant correlation signal is detected and transduced. The inventive correlator is based on an alpha-stable distribution and, in comparison with conventional alpha-stable distribution-based correlators, can more effectively operate in a realm wherein alpha is less than one.

Abstract: This invention features an improved technique for search and track surveillance. In this invention, distinct and random (in both space and time) signal beams are simultaneous transmitted from an array of transmitter source elements in a manner to cover all sectors about a source location. In addition, countermeasures against a system according to the invention are difficult because the signal waveforms for each beam are distinct and random, making prediction of any signal waveform for any beam very unlikely. An array of receiver sensor elements is provided to receive signals that are scattered from remote objects and may or may not be co-located with and share the elements of the source array element. The scattered signals are received and processed to yield the direction and range of the remote objects.

Abstract: The present invention relates to a radar system having means (12) for producing a code, means (18) for modulating a transmission signal in a transmit branch, using the code, means (32) for delaying the code, means (20) for modulating a signal in a receive branch, using the delayed code, and means (26) for mixing a reference signal with a receiving signal, the modulation of one of the signals being performed by an amplitude modulation (ASK; “amplitude shift keying”) and the modulation of the other signal by a phase modulation (PSK; “phase shift keying”). Furthermore, a radar system is proposed in which blanking of phase transitions is provided. The present invention also relates to methods which may advantageously be carried out, using the radar systems according to the present invention.

Abstract: A ROSAR wire detection method is based upon ROSAR focusing of entire segments of wire. By generating a wire reference signal comprised of a sum of coherent reference signals, the basis for reliable wire detectability is provided.

Abstract: A system and method for suppressing ground clutter in avionics weather radars which includes automatically making multiple scans, closely spaced in time and space, and comparing the returning signals to known ground return signals over known tilt angle variations.

Abstract: A radar performs accurate and appropriate pairing even if peaks of approximately identical signal intensities or even if a plurality of peak groups having identical representative beam bearings exist in the frequency spectrum. First, the peak frequency of a peak which appears in the frequency spectrum is determined for each of an up-modulating interval and a down-modulating interval in predetermined beam bearings, and signal-intensity profiles in the beam bearings are extracted with regard to a plurality of beam portions which are adjacent to the beam bearings. Next, the correlation level between the signal-intensity profiles at the up-modulating interval and the down-modulating interval is determined, and pairing is performed in sequence starting from the profiles having a higher correlation level.

Abstract: A method of processing reply signals received in response to an interrogation by a secondary surveillance radar system. The method includes the steps of receiving a reply signal from each of a plurality of targets, and enabling each of a plurality of target mode blocks having a predefined mode to select from the reply signals. The method further includes the step of correlating the selected reply signal to the target mode block that selected same.

Abstract: To suppress interfering stationary targets in radar source data, a STAP filtering method is used. Filtering coefficients are determined, and filtering of the data takes place, in the frequency domain; the process is therefore limited to a few computing operations per matrix element of the range/Doppler matrix. Since, by means of the STAP filter according to the invention, the optimal filtering characteristics can be implemented, the stationary target suppression also functions in the range of the minor lobes of the antenna. Therefore, data of individual adjacent channels (L/R, left/right) can be processed as well as summation and difference signals (&Sgr;/&Dgr;).

Abstract: The pulse center detector (PCD) produces an amplitude-independent center-triggered range output for precision radar rangefinders and TDR systems. Pulse center triggering is accomplished by triggering leading-edge and trailing-edge detectors and summing the outputs to produce a computed center-triggered result. Since the occurrence time of a pulse center does not vary with amplitude, the PCD is amplitude-independent. The PCD overcomes limitations of prior automatic pulse detectors, such as the inherent latency of a constant fraction discriminator (CFD) and the uncertainty of a time-of-peak (TOP) detector. The PCD can be implemented with a single analog component—a comparator—and thus requires appreciably fewer analog components than prior automatic detectors while providing lower jitter. Applications include radar and TDR tank gauges, and radar rangefinders for robotics and automotive applications.

Abstract: A system for determining the scan type of a signal, such as a radar signal, includes a scan detector, a transformer (e.g., an FFT algorithm), a correlator, and a decision block. The signal is received and processed by the scan detector. The scan detector provides an envelope signal, representing the scan type of the received signal. The envelope signal is transformed, typically from a time domain signal to a frequency domain signal, by any of several processes including a Fourier transform, a Laplace transform, an FFT, or a DFT. The transformed envelope signal is compared to several scan data sets by the correlator. Each scan data set represents a particular scan type. If the decision block determines that the comparison between the transformed envelope signal and a scan data set meets (or exceeds) a degree of similarity, the scan type of the received signal is determined to be the scan type of that scan data set.

Abstract: First-arriving-pulse detector (FAP) circuitry includes a correlator circuitry and a threshold circuitry. The correlator circuitry correlates a received signal with a template signal to provide an output signal. The threshold circuitry provides a first-arriving-pulse signal depending on the relative values of the output signal of the correlator circuitry and a threshold signal.

Abstract: An ultratight coupling method generates navigation error state information from an integration Kalman filter for updating the navigation solution based upon inertial measurement data and computes pseudorange and pseudorange rate data from the navigation solution and from ephemeris data, to generate the prompt, early and late replica signals that drive the signal correlators having quadrature outputs samples by a federation of Kalman prefilters providing errors residuals to the integration Kalman filter in a closed coupled tracking loop. The coupled tracking loops offer improved tracking of the received signal based upon updated navigation solution.

Abstract: In a method for operating a rotating synthetic aperture radar system that works with pulse frequency or in FM-CW operation in order to detect, penetrate and evaluate objects that are located vertically below the helicopter carrying the ROSAR device, pixels are determined using their own specific doppler histories.

Abstract: The invention relates to a method for calibrating a smart-antenna array of a wireless access system using TDD, which antenna array comprises antenna elements with a transmit and a receive branch each. In order to enable a time stable calibration, it is proposed that at least some of the antenna elements are selected in turns to be employed for transmitting broadcast messages. This provides time periods in which only one of said elements is transmitting. Each transmit branch is connected to at least one of the receive branches of another element, signals transmitted via these connections being evaluated for calibration. If receive branches are connected to transmit branches of several elements, it is ensured with the proposed selection that during the broadcast periods these receive branches receive at the most a signal from one element, thus avoiding the need for switches. The invention equally relates to a corresponding radio transceiver unit and a corresponding calibration system.

Abstract: A transmitted signal and a received signal are combined and the combination is expected to determine whether or not a target signal is present. Either the transmitted signal or the received signal is combined with an auxiliary signal containing a range of frequencies corresponding to an anticipated Doppler shift, so that an output of the combined transmitted and received signal will be present only if a target signal exhibiting a Doppler shift within the anticipated range is present. The auxiliary signal preferably comprises finite-duration signal portions of different types so as to provide a substantially uniform frequency response throughout the selected range.