Mission instruments development for Japanese ERS-1

Adv. Space Res. Vol. 12, No.7, pp. (7)319-(7)322, 1992 Printed in Great Britain. All rights reserved.

0273—1177/92 $15.00 Copyright © 1992 COSPAR

MISSION INSTRUMENTS DEVELOPMENT FOR JAPANESE ERS-1 I. Kudo,’~’H. Fujisada,* Y. Kato,* S. Hashimoto** and H. Hino~ * Electrotechnical Laboratory, AJST, MITI, 1-1-4 Umezono, Tsukuba, Ibaraki 305, Japan ** Japan Resources Observation System Organization, 3-15-3 Nishi-Shinbashi, Minato-ku, Tokyo 105, Japan

ABSTRACT An optical sensor (OPS) and a synthetic aperture radar (SAR) will be boarded on the Japanese Earth Resources Satellite. The OPS has 8-channel spectral bands including 4 SWIR bands and a stereoscopic band with the base-to-height ratio = 0.3 . The main features of the SAR are L-band, H-H polarization, moderate off-nadir angle and high resolution. The definitions of specifications for both sensors and development status are described. INTRODUCTION In response to the requirements of the user community in non-renewable resource exploration, the Ministry of International Trade and Industry (MITI) has initiated research and development of the first Japanese Earth Resources Satellite (JERS) with the Science and Technology Agency. The MITI shares a mission payload which consists of the SAR, OPS , a data recorder and a data transmitter while STA is developing the satellite platform and a launching vehicle. The Japan Resources Observation System Organization (JAROS) has succeeded the efforts of RRSS and now develops the flight model of mission instruments. The satellite will be launched aboard a 11-1 launch vehicle from the Tanegashima Space Center in early 1992. The JERS-l will operate from a 568km circular sun-synchronous orbit, imaging the same 75km swath of the earth surface every 44 days. Figure 1 shows the flight segment. The spaceborne SAR has the advantages of all-weather day-and-night operation and high resolution in geologic mapping. On the other hand, the OPS covers a different portion of the electromagnetic spectrum which is used to identify and characterize the sources of radiation. The spectral band should be selected to provide maximum discrimination for nonrenewable resource exploration purposes. The satellite imagery data will be used by geologists constructing a three-dimensional geologic model . The specification for these mission instruments were carefully determined in response to the user community. The purposes of this paper are to present the development status sensors with specifications.

MDT Antefl~~ S~~lite Sp,r~ Earth

Fig.

1 JERS Flight (7)319

11.9=

(X ,xi~ ~ 1l.lrfl (Y axis)

Segment

of

these

I. Kudo et a!.

(7)320

USER REQUEST AND SENSOR SPECIFICATION Prior tions

to hardware development, simulation and analysis of sensor were undertaken.

specifica-

Synthetic Aperture Radar The strong dependence of radar backscatter on changes in surface roughness, slope, or the dielectric constant makes It possible to map geological features for non-renewable resource exploration. Really, the usage of’ radar imagery for commercial purposes has been started. Since the discovery of new fuel and mineral fields will be essential toward the end of this century, a global mapping of the earth’s structural features will be prerequisite for more efficient assessment of the world petroleum and mineral reserves. The SAR is particularly effective in the area of persistent rainfall or cloud cover. In order to clarify user requirement, the incident angle, spatial resolution, signal -to- noise ratio, quantization, and the number of looks were examined using airborne SAR data. Requirements of low distortion and high spatial resolution recommended an off-nadir angle from 40 to 50 and resolution from lOm to 2Om. Since SAR is an instrument of large power consumption and high data rate, the determination of the specification requires consideration of the satellite’s constraints . The final specifications were established as shown In Table 1. Though the off-nadir angle of 35 was lower than the user request, it was decided so because the signal -tonoise ratio would be degraded with Increasing off-nadir angle. Parametric

studies

using SAR-58O data concluded that ERS-l data would be effective

the extraction of topographical features and even for the discrimination textural differences. Simulated data were compared with SIR-B, as shown Fig.2.

CHL

E

TE

CA

E

MU

VITE

KA

ITE

Ui

0

Lii -J Lii

(a) Degraded from SAR-580 Data

w MON

RILLONITE

.~1 Lii

AL

E

4

OA No.

~

~

~

1.40 BAND No.

(b) Fig.

1.60

1.80

WAVELENGTH(JLm)

.8

2.00

2.20 2.40 WAVELENGTH Dim) BAND No. WAVELENGTH(um)

1 2 3

0.52—0.60 0.63—0.69 0.76—0.86

5 6 7

1.60-~1.71 2.01—2.12 2.13—2.25

4

0.76—0.86(STEREO)

8

2.27—2.40

SIR-B

2 SAR

Simulation

Fig.

3

SWIR Spectral

Bands

for of in

(7)321

JapaneseERS-l

TABLE 1 SAR Characteristics CENTER FREQUENCY

1.275GHz±2OkHz

ANTENNA GAIN

33.5dB AT

BAND WIDTH

15MHz

s/A

14dB

POLARIZATION

N—H

PULSTH LENGTH

15~s

OFF—NADIR ANGLE

35.21DEG

PRF

1505.8, 1530.1

RESOLUTION

RANGE

18m

1555.2

AZIMUTH

18m(3 LOOKS)

1606.0

QUANTIZATION

3BITS

OUTPUT DATA RATE

60MBPS

TRANSMIT POWER

BEAN

CENTER

1581.1

1.1-1.5kW

TABLE 2 OPS Characteristics OBSERVATION WAVE LENGTH (pm)

VNIR

0.52—0.60 0. 63—0. 69 0.76—0.86 0.76—0.86 (STEREO)

SWIR

1.60—1.71 2.01—2.12 2.13—2.25 2.27—2.40

STEREO ANGLE

15.3~ (B/H

GROUND RESOLUTION

18.3m

PIXEL NUMBER/BAND

4096

SCANNING WIDTH

75km

OUTPUT DATA RATE

30Mbps

SAMPLING FREQUENCY

3.46ms/LINE

=

0.3>

24.2m

x

x

2CH

Optical Sensor As requests from the petroleum resource exploration community, spatial resolution below 25m , solar angle below 40 degrees, stereoscopic base-toheight ratio above 0.3, and dynamic range above 6 bits were submitted. After these recommendations were considered with the constraints of the satellite resources, the final bands were decided as shown in Table 2 . Carbonate rock can be discriminated as a petroleum reservoir rock, as shown in Fig. 3 Forward/Nadir stereoscopic observation helps in the extraction of lineanents and this function was also included in the specification. It is thought that stereo imagery will be a unique feature of this satellite. Simultaneous data transmission of all 8 bands is required and it enables napping to be completed in a short time. MISSION INSTRUMENTS Figure 4 shows a block diagram showing MITI’s share. Fabrication of all instruments has been completed and the instruments are ready for integration into the JERS-platform. SAR This subsystem consists of an antenna which is folded during the launch and deployed on orbit, TX/RX and a signal conditioner. A solid state amp unit in TX will be able to output a maximum of 1.5 KW.

Optical Sensor This subsystem consists of VNIR and SWIR. For realizing the high resolution requirement, both images are taken using the pushbroon scanning mode.

(7)322

I. Kudo eta!.

r

SYNTHETIC APERTURE RADAR(SAR>

TRANSMITTER!

SICNAL

RECEIVER

PROCESSOR

:

I

TTT~1 ~

RADIOMETER

I

RAIOMETER

MISSION DATA TRANSMITTER(MDT) .

LTTT L_~

-

IRECORDER~MDR)

Fig. 4 Mission Instruments

VNIR The VNIR optical telescope adopts a refractive design and four dichroic prisms are used for spectral separation. As a detector, the 4096-pixel silicon CCD was developed. The sensor image element size is 7x7 microns. The stereoscopic view is obtained with forelooking and nadir- looking detectors inside a single optical system . This

methods makes stereo image acquisition in the same orbit path possible. SWIR

A

reflector-refractive

requirement.

Large

telescope was selected for the

amounts

of heat

generated

by the

large

image

4096 silicon

plane

Shottokey

barrier IRCCD detector must be rejected. The only solution is a Stirling cycle refrigerator . This adoption of an active cooler on a civil operational satellite will be the first attempt in the world. The sensor image element size is lOx2O microns . Four channels are installed on a single chip and the detector covers a spectrum range from 1.5 to 2.5 microns.Autofodus mecha-

nisms

for both VNIR and SWIR are installed. Normal or higher gain . In-orbit calibration of the optical system is using internal lamps for VNIR and SWIR. adjusted by command

can be possible

Data Recorder and mission data transmitter The recorder which is employed for this mission was originally developed for SPOT and improved by ODETICS. The major item changed is the recording speed from 50 Mbps to 60 Mbps, the recording capacity from 66 Gbits to 72 Gbits. The recording time is reduced to 20 minutes. On the other hand, the mission data transmitter is dedicated to imagery data transmission. Telemetry data from the satellite CDMS use a satellite transmission system. Either real time imagery or stored data can be transmitted using the 8 GHz band carrier. Two 20W TWT tubes are employed for increasing the reliability. MISSION OPERATION AND DATA DISTRIBUTION For JERS-l, the period of engineering evaluation may extend through several months. Operational data from JERS-1 can be expected after the initial evaluation period has been completed. The spacecraft will be controlled and the image data will be received from Hatoyama Station NASDA, Japan . In addition foreign ground stations, Fairbanks and Kiruna will receive imagery and associated telemetry data. At the Earth Observation Center (EOC), NASDA, the

sensor

data

radiometric

are received and quality checked, cloud corrections

are applied

cover

is

quantified,

and geometric correction coefficients are

generated. Selected images have geometric corrections applied and are converted into various products for users. The products include CCT, film and FD. The ERSDAC is an organization responsible for disseminating the satellite data for non-renewable resource users. For other fields, RESTEC may be

contacted. For aiding data usage, sensors protoflight data about sensitivity be contained The

satellite

analysis days,

radiometric

dynamic band to band registration and geometric accuracy in the databook which will be distributed. ,

will

concluded

on the other

be operated to map the entire land area. Global

that SAR data acquisition could be completed hand OPS would require 352 days.

will

coverage

after

210