PALSAR Sensor

The Phased Array type L-band Synthetic Aperture Radar (PALSAR) is an active microwave sensor using L-band frequency to achieve cloud-free and day-and-night land observation. It provides higher performance than theJERS-1's synthetic aperture radar (SAR). Fine resolution in a conventional mode, but PALSAR will have another advantageous observation mode. ScanSAR, which will enable us to acquire a 250 to 350km width of SAR images (depending on the number of scans) at the expense of spatial resolution. This swath is three to five times wider than conventional SAR images. The development of the PALSAR is a joint project between JAXA and the Japan Resources Observation System Organization (JAROS).


PALSAR Characteristics

Mode Fine ScanSAR Polarimetric
(Experimental mode)*1
Center Frequency 1270 MHz(L-band)
Chirp Bandwidth 28MHz 14MHz 14MHz,28MHz 14MHz
Polarization HH or VV HH+HV or VV+VH HH or VV HH+HV+VH+VV
Incident angle 8 to 60deg. 8 to 60deg. 18 to 43deg. 8 to 30deg.
Range Resolution 7 to 44m 14 to 88m 100m
(multi look)		 24 to 89m
Observation Swath 40 to 70km 40 to 70km 250 to 350km 20 to 65km
Bit Length 5 bits 5 bits 5 bits 3 or 5bits
Data rate 240Mbps 240Mbps 120Mbps,240Mbps 240Mbps
NE sigma zero *2 < -23dB (Swath Width 70km) < -25dB (Swath Width 60km) < -25dB < -29dB
S/A *2,*3 > 16dB (Swath Width 70km)
> 21dB (Swath Width 60km)		 > 21dB > 19dB
Radiometric accuracy scene: 1dB / orbit: 1.5 d

Note: PALSAR cannot observe the areas beyond 87.8 deg. north latitude and 75.9 deg. south latitude when the off-nadir angle is 41.5 deg.
* 1 Due to power consumption, the operation time will be limited.
* 2 Valid for off-nadir angle 34.3 deg. (Fine mode),
 34.1 deg. (ScanSAR mode),
 21.5 deg. (Polarimetric mode)
* 3 S/A level may deteriorate due to engineering changes in PALSAR.


References:
- Daichi, Advance Land Observing Satellite.

AVNIR-2 Sensor


The Advanced Visible and Near Infrared Radiometer type 2 (AVNIR-2) is a visible and near infrared radiometer for observing land and coastal zones. It provides better spatial land-coverage maps and land-use classification maps for monitoring regional environments. AVNIR-2 is a successor to AVNIR that was on board the Advanced Earth Observing Satellite (ADEOS), which was launched in August 1996.
Its instantaneous field-of-view (IFOV) is the main improvement over AVNIR. AVNIR-2 also provides 10m spatial resolution images, an improvement over the 16m resolution of AVNIR in the multi-spectral region. Improved CCD detectors (AVNIR has 5,000 pixels per CCD; AVNIR-2 7,000 pixels per CCD) and electronics enable this higher resolution. A cross-track pointing function for prompt observation of disaster areas is another improvement. The pointing angle of AVNIR-2 is +44 and - 44 degree.


AVNIR-2 Characteristics

Number of Bands
4
Wavelength
Band 1 : 0.42 to 0.50 micrometers
Band 2 : 0.52 to 0.60 micrometers
Band 3 : 0.61 to 0.69 micrometers
Band 4 : 0.76 to 0.89 micrometers
Spatial Resolution
10m (at Nadir)
Swath Width
70km (at Nadir)
S/N
>200
MTF
Band 1 through 3 : >0.25
Band 4 : >0.20
Number of Detectors
7000/band
Pointing Angle
- 44 to + 44 degree
Bit Length
8 bits

Note: AVNIR-2 cannot observe the areas beyond 88.4 degree north latitude and 88.5 degree south latitude.


References:
- Daichi, Advance Land Observing Satellite.

PRISM Sensor


The Panchromatic Remote-sensing Instrument for Stereo Mapping (PRISM) is a panchromatic radiometer with 2.5m spatial resolution at nadir. Its extracted data will provide a highly accurate digital surface model (DSM).

PRISM has three independent optical systems for viewing nadir, forward and backward producing a stereoscopic image along the satellite's track. Each telescope consists of three mirrors and several CCD detectors for push-broom scanning. The nadir-viewing telescope covers a width of 70km; forward and backward telescopes cover 35km each.

The telescopes are installed on the sides of the optical bench with precise temperature control. Forward and backward telescopes are inclined +24 and -24 degrees from nadir to realize a base-to-height ratio of 1.0. PRISM's wide field of view (FOV) provides three fully overlapped stereo (triplet) images of a 35km width without mechanical scanning or yaw steering of the satellite. Without this wide FOV, forward, nadir, and backward images would not overlap each other due to the Earth's rotation.


PRISM Characteristics
Number of Bands

1 (Panchromatic)
Wavelength

0.52 to 0.77 micrometers
Number of Optics

3 (Nadir; Forward; Backward)
Base-to-Height ratio

1.0 (between Forward and Backward view)
Spatial Resolution

2.5m (at Nadir)
Swath Width

70km (Nadir only) / 35km (Triplet mode)
S/N

>70
MTF

>0.2
Number of Detectors

28000 / band (Swath Width 70km)
14000 / band (Swath Width 35km)
Pointing Angle

-1.5 to +1.5 degrees
(Triplet Mode, Cross-track direction)
Bit Length

8 bits

Note: PRISM cannot observe areas beyond 82 degrees south and north latitude.


Observation Modes

Mode 1

Triplet observation mode using Forward, Nadir, and Backward views (Swath width is 35km)
Mode 2

Nadir (70km) + Backward (35km)
Mode 3

Nadir (70km)
Mode 4

Nadir (35km) + Forward (35km)
Mode 5

Nadir (35km) + Backward (35km)
Mode 6

Forward (35km) + Backward (35km)
Mode 7

Nadir (35km)
Mode 8

Forward (35km)
Mode 9

Backward (35km)


















References:
- Daichi, Advance Land Observing Satellite.

ALOS Characteristic

Launch Date
Jan. 24, 2006
Launch Vehicle
H-IIA
Launch Site
Tanegashima Space Center
Spacecraft Mass
Approx. 4 tons
Generated Power
Approx. 7 kW (at End of Life)
Design Life
3 -5 years
Orbit
Sun-Synchronous Sub-Recurrent

Repeat Cycle: 46 days
Sub Cycle: 2 days

Altitude: 691.65 km (at Equator)

Inclination: 98.16 deg.
Attitude Determination Accuracy
2.0 x 10-4degree (with GCP)
Position Determination Accuracy
1m (off-line)
Data Rate
240Mbps (via Data Relay Technology Satellite)
120Mbps (Direct Transmission)
Onboard Data Recorder
Solid-state data recorder (90Gbytes)

References:
- Daichi, Advance Land Observing Satellite.

About ALOS


ALOS Overview

The Japanese Earth observing satellite program consists of two series: those satellites used mainly for atmospheric and marine observation, and those used mainly for land observation. The Advanced Land Observing Satellite (ALOS) follows the Japanese Earth Resources Satellite-1 (JERS-1) and Advanced Earth Observing Satellite (ADEOS) and will utilize advanced land-observing technology. ALOS will be used for cartography, regional observation, disaster monitoring, and resource surveying.

The ALOS has three remote-sensing instruments: the Panchromatic Remote-sensing Instrument for Stereo Mapping (PRISM) for digital elevation mapping, the Advanced Visible and Near Infrared Radiometer type 2 (AVNIR-2) for precise land coverage observation, and the Phased Array type L-band Synthetic Aperture Radar (PALSAR) for day-and-night and all-weather land observation. In order to utilize fully the data obtained by these sensors, the ALOS was designed with two advanced technologies: the former is the high speed and large capacity mission data handling technology, and the latter is the precision spacecraft position and attitude determination capability. They will be essential to high-resolution remote sensing satellites in the next decade. ALOS have been successfuly launched on an H-IIA launch vehicle from the Tanegashima Space Center, Japan.


ALOS Objective

ALOS is one of the largest Earth observing satellites ever developed. Its objectives are:
  • To provide maps for Japan and other countries including those in the Asian-Pacific region (Cartography)
  • To perform regional observation for "sustainable development", harmonization between Earth environment and development (Regional Observation),
  • To conduct disaster monitoring around the world (Disaster Monitoring),
  • To survey natural resources (Resources Surveying),
  • To develop technology necessary for future Earth observing satellite (Technology Development)
References:
- Daichi, Advance Land Observing Satellite.