anced Visible and Near-Infrared Radiometer):
AVNIR is a NASDA core sensor, an optoelectronic scanning radiometer using CCD detectors. Objective: Land and coastal zone observations, measurement of reflected sunlight from the Earth's surface. AVNIR is comprised of two units, SRU (Scanning Radiometer Unit) containing all the optical components (a catadioptric Schmidt telescope system is used, the spectrum is dispersed by a prism and interference filter), and ELU (Electronic Unit). 18) 19) 20)
Spectral range: 5 bands from 0.42 - 0.89 µm (multispectral bands: 0.42-0.50, 0.52-0.60, 0.61-0.69 and 0.76-0.89 µm, panchromatic band (visible): 1 band 0.52-0.69 µm). Spatial resolution: multispectral bands: ~16 m (IFOV=20 µrad), panchromatic band: about 8 m (IFOV =10 µrad). Swath width = 80 km (FOV=5.7º). Observation requirements: regional observation according to user requests; simultaneous multispectral and panchromatic operation. 21) 22)
The AVNIR instrument has the capability to tilt the observation field by ±40º about the across-track axis. The 0.42-0.50 µm band is useful for coastal zones and lakes. The scanning radiometer unit uses a catadioptric Schmidt optical system (telescope) to reduce aberration in a wide field of view. Calibration of sensor using solar light and internal lamps. The radiometric absolute accuracy is ±10%, the onboard calibration accuracy =±5%. The large linear array CCDs offer 5,000 and 10,000 detector elements for high spatial resolution. Instrument mass=250 kg, power=300W.
Figure 6: The observation geometries of the AVNIR instrument
Figure 7: Illustration of the AVNIR instrument (image credit: NASDA)
Figure 8: Block diagram of the AVNIR instrument (image credit: NASDA)
Figure 9: AVNIR image of the island reefs in the Great Barrier Reef of northeast Australia (image credit: JAXA)
NSCAT (NASA Scatterometer):
NSCAT is a NASA/JPL sensor. Objective: Measurement of surface wind speeds and directions over the global oceans, coverage every two days under all weather and cloud conditions. NSCAT is a microwave radar instrument (a fan-beam Doppler scatterometer), using an array of six antennas that radiate microwave pulses at a frequency of 13.995 GHz across broad regions of the Earth's surface.
An array of six, 3 m long antennas scan two swaths of 600 km width each, one band to each side of the flight path, separated by a gap of 330 km at nadir. Wind speed accuracy = 2 m/s (rms), direction accuracy = 20º (rms), resolution = 50 km; antenna polarization: 6 V, 2 H; antenna beam width=25º (3 dB broad beam) =0.42º (3 dB narrow beam); instrument mass = 280 kg; power=240 W; data rate = 3.2 kbit/s; peak transmit power=110 W; pulse width=5 ms; PRF=62 Hz. Operation requirements: continuous operation for global observation of the oceans (about 190,000 wind measurements/day). Note: NSCAT is an upgraded version of the Radar Scatterometer (SASS) on SEASAT. 23) 24) 25)
Figure 10: Illustration of the NSCAT antenna radiation pattern geometries (image credit: NASA)
NSCAT transmits microwave pulses and receives a backscattered echo from the ocean surface. Changes in wind velocity cause changes in ocean surface roughness, modifying the radar cross section of the ocean and the magnitude of the backscattered power. Multiple collocated measurements acquired from several directions can thus be used to solve for wind speed and direction simultaneously.
Table 3: NSCAT instrument performance parameters
Figure 11: Schematic of NSCAT instrument (image credit: NASA)
TOMS (Total Ozone Mapping Spectrometer):
TOMS is a NASA/GSFC sensor. Objective: Observation of total ozone changes, evaluation of changes in UV radiation and the observation of sulfur dioxide. Measurement wavelengths: 308.6, 312.5, 317.5, 322.3, 331.2 and 360 nm with 1 nm bandpass. Swath width: 2795 km. IFOV= 50 km at nadir; cross-track scan = 111º (37 3º steps). Operation requirements: global observation of illuminated part. TOMS mass=34 kg, power=24 W, data rate=700 bit/s.
TOMS measures the albedo of the Earth's atmosphere at six narrow spectral bands in the near-ultraviolet regi