P-band Radar

P-band Radar

The AirMOSS radar will be a modification of the L-band radar in NASA's Uninhabited Aerial Vehicle Synthetic Aperture Radar (UAVSAR) program.

The NASA/JPL UAVSAR is a pod-based repeat-pass polarimetric SAR that currently operates in L-band (1.2 Ghz). The AirMOSS radar replaces the L-band front-end electronics and antenna with components that operate at P-band. The major components of the P-band front-end electronics are based on AIRSAR and GeoSAR heritage, and the P-band antenna utilizes the GeoSAR P-band antenna design.

UAVSAR radar pod
 

AirMOSS utilizes a passive dual-polarized array antenna based on the GeoSAR P-band antenna design to take advantage of the good polarization isolation over the bandwidth of 280 to 440 MHz.

P-band antenna mounted in the pod
 

The radar utilizes the L-band RF electronics and an arbitrary waveform generator (AWG) from UAVSAR. The L-band transmit pulse is down-converted to P-band by mixing it with a tone from a direct digital synthesizer (DDS). The P-band transmit pulse is then amplified and sent to either the horizontal (H) or the vertical (V) polarization channel of the passive antenna. The transmit bandwidth is determined by the AWG and the selection of one of four filters (6, 20, 40, or 80 MHz) in a filter bank.

The radar has two identical receive chains. Both the H and the V radar returns are up-converted to L-band by mixing them with the same tone from the DDS as was used on transmit. The radar return is filtered using an identical filter bank as on transmit and then enters the UAVSAR receive electronics.

Frequency selectability
 

The DDS tone frequency, the filter choice within the filter bank, and the polarization of the antenna during transmit can be commanded on a pulse-to-pulse basis for a predefined sequence of up to 16 pulses, which is repeated over and over throughout a data collection. For example, it is possible to collect simultaneously data to form fully polarimetric SAR images for a low frequency 20 MHz sub-band and a high frequency 20 MHz sub-band by defining a 4 pulse sequence as shown in the figure. Note that this is not currently planned for AirMOSS operations.
 

Key Radar Instrument Parameters

  UAVSAR AirMOSS
Frequency band L-band P-band
Frequency range (MHz) 1217.5 - 1297.5 280 - 440
Nominal bandwidth (MHz) 80 20
Selectable bandwidths (MHz) 80 6, 20, 40, or 80
Nominal slant range resolution (m) 1.8 7
Azimuth resolution (m) 0.8 0.8
Polarization Quad-pol Quad-pol
Nominal altitude 12,500 m (41 kft) 12,500 m (41 kft)
Pulse length (µs) 5 - 50 5 - 50
Peak transmit power (kW) 3.1 2.0
Nominal spatial posting (m) 6 10
Nominal range swath (km) 22 7
Look angle range 25 - 65° 25 - 45°
Noise equivalent σ (dB) < -50 < -40

 

The P-band radar flies on the a Gulfstream-III (G-III) jet operated by JSC.