CBERS-4A (China-Brazil Earth Resources Satellite-4A)
The CBERS program was born out a unique partnership between Brazil and China in the space technical and scientific sector for the primary remote sensing data generation technology, this partnership agreement involves INPE (National Institute for Space Research) and CAST (China Academy of Space Technology). 1)
The program is a family of remote sensing satellites CBERS (CBERS-1 and 2, CBERS-3 and 4) that brought significant scientific advances to Brazil. The INPE, using only the CBERS-4, has distributed for free over the internet, approximately 90,000 images. These images are being used in important fields such as controlling deforestation and burning in the Amazon, the monitoring of water resources, agriculture, urban growth, land use and education. They are also critical for large strategic national projects such as Measurement of Deforestation by Remote Sensing (PRODES) and Brazilian Real-Time Deforestation Detection (DETER) and monitoring of sugarcane areas, among others.
Both systems, DETER and PRODES, are affected by the high frequency of clouds over the Amazon region. So, to ensure that the monitoring and measurement of deforestation is feasible, it is necessary to have remote sensing data in spatial and temporal resolutions compatible with these phenomena. 2)
The requirement for a high rate of revisits and the need of controlling and data reception of other remote sensing satellites available in Brazil, for example, the Amazonia-1 – it due to be concluded in 2019 - (5 days to revisit) impose challenges for the ground segment. As in previous missions, the Ground Segment is responsible for tracking and controlling of the satellites CBERS during the routine phase, including the orbit adjustment maneuvers to maintain the proper phase, that are made by Brazil, and by China, in alternating periods.
The Ground Segment has more and more served as cross support and interoperability to space agencies, which requires an appropriate architecture to support them. The architecture proposal is based on Dynamic Management of the Space Link Extension (SLE) Protocol Services. In this scenario, the CCSDS recommends normalizing cross support services between the space agencies aiming at interoperability and standardization of data transfer services.
Mission and Project Description: The CBERS-4A objective is to provide remote sensing images to observe and monitor vegetation - especially deforestation in the Amazon region - the monitoring of water resources, agriculture, urban growth, land use and education with a high revisit rate and considering the synergy with the existing programs PRODES and DETER.
CBERS-4A mission is an example of cooperation among the main areas of INPE. This project involves the Engineering and Space Technology; Satellite Tracking and Controlling, and Integration and Testing Laboratory as providers of solutions and the Earth Observation and Earth System Science areas as users.
The data from the CBERS Program are available to users in the online catalog from INPE. The free offer of satellite images benefits the government's own territory management system, research universities and the development of private enterprises.
The specifications of the Sino-Brazilian satellite -remote sensing satellite medium resolution provided optical payloads operating in the visible spectrum with resolutions in the range of 2 to 60 meter - are similar to remote sensing programs most used worldwide, such as Landsat (United States), ResourceSat (India) and Copernicus (European Union).
The configuration of the CBERS-4A is similar to those of CBERS-3 & 4 satellites, with improvements to accommodate the new Chinese Imager camera that has superior quality in geometric and spectral resolution.
The satellite consists of two independent modules: a service Module and a Payload module, which houses image cameras and recording equipment and transmission of the image data.
Figure 1: Artist's rendition of the CBERS-4A satellite (image credit: INPE)
In addition to the subsystems that make up the satellite, each country is responsible for providing a set of test equipment used to test the satellite during the assembly phase, Integration and Test (AIT).
Table 1: Differences between the satellites of the 1st and 2nd generation
Launch: The CBERS-4A/ZiyuanI-4A (CNSA S/C designation) satellite was launched on 20 December 2019 (03:22 UTC) from TSLC (Taiyuan Satellite Launch Complex) located in north China's Shanxi province, with a Long March 4B ( LM-4B) launch vehicle. 3)
Figure 2: A Long March-4B launch vehicle launched the China-Brazil Earth Resource Satellite-4A (CBERS-4A) from the Taiyuan Satellite Launch Center, Shanxi Province, northern China, on 20 December 2019, at 03:22 UTC (11:22 local time), video credit: SciNews
The CBERS-4A will replace CBERS-4, which was launched in 2014, to improve the resolution of the remote-sensing data, said CNSA.
Orbit: Sun-synchronous near-circular orbit, altitude =628.6 km, inclination= 97.9º, LTDN (Local Time on Descending Node) at 10:30, repetition cycle = 31 days, orbital period = 97.25 minutes. The interval of three days between adjacent strips remains the same pattern as the previous imaging CBERS, and allows phenomena occurring in areas adjacent two imaging ranges may be viewed in a short time.
• ETRSS-1 (Ethiopian Remote Sensing Satellite-1), a multispectral microsatellite (70 kg), developed in collaboration with CAST and ESSTI (Ethiopian Space Science and Technology Institute) with support of the Chinese government. Up to 20 Ethiopian aerospace engineers were involved in the preliminary and critical design and development of the satellite. The satellite will be used to monitor agricultural, water and urban development in Ethiopia.
• FloripaSat-1, a 1U CubeSat and a technology demonstration mission entirely developed by SpaceLab students at the Federal University of Santa Catarina (UFSC), Brazil. The payload is an amateur radio repeater, which can be used all over the globe in emergency and rescue situations.
• Tianquin-1/CAS-6, a Chinese microsatellite (35 kg), carrying su-payload for amateur radio communication and education.
• Weilai-1R, a Chinese microsatellite (~40 kg) for space science experiments and remote sensing by CCTV (China Central Television).
• Yuheng, a small satellite technology demonstration mission of NUDT (National University of Defense Technology), China.
• Shuntian, a small satellite technology demonstration mission of NUDT, China.
• Tianyan-1 / Yizheng-1 and Tianyan-2 / Yizheng-2. Two Chinese small technology verification satellites for for a future space-based gravitational wave detection constellation. Tianqin satellites will use inter-spacecraft laser interferometry to pick up the ripples in space-time, or gravitational waves, created by the collision of massive objects such as black holes.
Sensor complement: (MUX, WFI, WPM, DCS, SEM)
For the payload, Brazil is responsible for the Multispectral Camera (MUX), the Wide Field Imaging Camera (WFI), the Digital Data Recorder (DDR) and the Subsystem Data Collection (DCS), while China is responsible for the Data Transmitter System (DTS), Space Environment Monitor (SEM), Multispectral and Panchromatic Wide-Scan Camera (WPM) and Wiring (SYCS).
The CBERS-04A satellite is equipped with cameras for optical observations from around the globe, as well as a data collection and environmental monitoring services.
The application potential of a given sensor is a function of their spatial resolution characteristics, temporal resolution, and spectral and radiometric characteristics.
MUX (Multispectral Camera)
MUX is a Brazilian imager providing imagery of 16 m resolution at nadir with revisits of 31 days. Scanning technique: pushbroom with a swath width of 120 km, possible to be pointed within a field of regard of ± 500 km. MUX has a mass of 115 kg, a power consumption of 66 W and a data rate of 68 Mbit/s.
Table 2: Spectral bands of the MUX camera
WFI (Wide Field Camera)
WFI is a Brazilian imager providing imagery of 55 m resolution with revisits of 5 days. Scanning technique: pushbroom with a swath width of 800 km. The instrument has a mass of 43 kg, a power consumption of 70 W and a data rate of 50 Mbit/s.
Table 3: WFI requirements
WPM (Multispectral and Panchromatic Wide-Scan Camera)
WPM is a Chinese imager (developed at CAST) providing panchromatic imagery with 2 m resolution and multispectral RGB imagery of 8 m resolution. Scanning technique: Pushbroom, swath 60 km, possible to be pointed within a field of regard of ± 500 km. WPM has a mass of 263 kg, a power consumption of 80 W and a data rate of 240 Mbit/s. The WPM has focal plane adjustment and on-orbit calibration capabilities.
Table 4: Spectral bands of PanMUX camera
DCS (Data Collection System)
Beside the cameras, CBERS 3&4 will have the DCS (Data Collection System) and the SEM (Space Environment Monitor). The DCS is provided by INPE and the SEM is provided by CAST (Chinese Academy of Space Technology).
Ground Segment (GS)
The Reception and Data Recording Station - ERG INPE, in Cuiabá, MT receives and continuously records the images transmitted by the CBERS satellites.
The station consists of two subsystems reception and two recording subsystems. The reception subsystems are basically constituted by the antenna dish 10 m in diameter operating in S-band and X-band, the antenna dish of 11.28 m in diameter is operating in X- band and the respective Radio Frequency equipment. The recording subsystem consists of two subsystems, whose recording capacity of each is of up to 160 Mbit/s, and the recording subsystem MATRA/CBERS intended for reception of CBERS images.
Figure 3: Overview of the CBERS-4A system elements (image credit: INPE)
Regularly received data are transferred to the Image Processing Center Imaging Division in Cachoeira Paulista, in São Paulo State, for further processing and dissemination to end users. Figure 4 shows details of the Reception and Recording Station in the ground system.
Figure 4: X-band reception and recording station (image credit: INPE)
TT&C Ground Station
The operation and control of the satellites CBERS program during the routine phase including the orbit adjustment maneuvers to maintain the proper phase are made now by Brazil, now by China, in alternating periods, according to a unified program of the Center Xian Control.
The CBERS ground segment supports the activities necessary to control the satellites and to achieve the objectives of its remote sensing missions. This includes the means for tracking, command and control of the satellites and receiving, storing, processing and distribution of the imagery.
The functions related to programming of the operations of the satellite cameras in response to user requests are made by the Mission Center in Cachoeira Paulista. However, the central element of all operations relating to the CBERS satellite and its mission control is the Satellite Control Center (SCC).
The Telemetry, Tracking and Command (TT&C) Ground Stations provide the link between the control personnel and the satellite; they are the stations used for the acquisition of raw data from the CBERS data collection system in S-band.
The Satellite Control Center receives a variety of satellite information that permits the operators to keep themselves fully informed about the status of the satellite equipment, allowing to perform the necessary actions to ensure its proper operation.
The TT&C Ground Stations (GS) of INPE were built in 1988 to support the Data Collecting Satellite-1 (SCD1), which was launched 1993. They operate in S-band and are located in the Brazilian cities of Cuiabá and Alcântara. TT&C GSs are in charge of establishing communication between the ground control system and the satellites monitored during the visibility periods.
Figure 5 shows the INPE's Ground Station: SCC and the main systems of the GS: RF Front End, Receiver, Antenna Control Unit (ACU) and Time & Frequency. The functions of TM, TC, Ranging Data (RG), Range Rate (RR) and the SLE Provider are based on the Integrated Baseband System (IBS). The IBS allows the implementation of Space Link Extension (SLE) services for cross support and the interoperability between space agencies.
Figure 5: INPE's Ground Station (image credit: INPE)
The SCC is responsible for planning and executing of all activities related to the satellites control and is the administrative headquarters. The SCC is located in the city of São José dos Campos, Brazil. The main functions of a SCC are: orbit and attitude control, maneuver calculations, operational payload configuration, and real-time monitoring of the satellite health.
Over the structure of the SCC is embedded a software system, SATellite Control System (SATCS); developed by the Ground Systems Development Division (DSS) of coordination of Space Engineering and Technology at INPE. The SATCS is designed to be easily configurable and customized to meet the requirements of different satellite types.
The imagery receiving stations and processing centers in Brazil and China are the backbone of receiving stations that can be installed in other countries to extend the potential coverage of CBERS.
1) Antonio Cassiano Julio Filho, Ana Maria Ambrosio, Mauricio Gonçalves Vieira Ferreirac, Geilson Loureiro, "The China-Brazil Earth Resources Satellite - CBERS-4A: A proposal for Ground Segment based on the Space Link Extension Protocol Services," Proceedings of the 70th IAC (International Astronautical Congress), Washington DC, USA, 21-25 October 2019, paper: IAC-19.B6.1.12, URL: https://iafastro.directory/iac/proceedings/IAC-19/IAC
2) Antonio Cassiano Julio Filho, Ana Maria Ambrosio, Maurício Gonçalves V. Ferreira, Eduardo WhitakerBergamini, "New Challenges for Dynamic Management of the Space Link Extension Protocol Services: The Amazonia-1 Satellite's Ground Segment,"Space Ops Conference, Marseille, France, 28 May - 1 June 2018, URL: https://arc.aiaa.org/doi/pdf/10.2514/6.2018-2315
3) "New China-Brazil earth resource satellite sent into space," Xinhuanet, 23 December 2019, URL: http://www.xinhuanet.com/english/2019-12/20/c_138645961.htm
The information compiled and edited in this article was provided by Herbert J. Kramer from his documentation of: "Observation of the Earth and Its Environment: Survey of Missions and Sensors" (Springer Verlag) as well as many other sources after the publication of the 4th edition in 2002. - Comments and corrections to this article are always welcome for further updates (firstname.lastname@example.org).