SIMA - Integrated System for Environmental Monitoring - developed in partnership between the Vale do Paraíba University and the National Institute of Space Research, is a set of hardware and software designed for data acquisition and real time monitoring of hydrological systems. It is composed of an independent system formed by an anchored buoy, in which sensors, data storage systems, battery and the transmission antenna are fixed. The data are collected in preprogrammed time intervals and are transmitted by satellite in quasi-real time for any user in a range of 2500 km from the acquisition point.

SIMA is formed by a platform which in some designs may be a toroidal float (left photo) or a larger structure (right photo). In the center of buoy platform there is a tower where are fixed the solar panel, meteorological sensors and the antenna. In a sealed structure (in the center of the buoy) a compartment housing the electronic system, battery and the satellite transmitter. The submerged sensors are connected to the electronics by sealed cables.

• aquatic systems are dynamics and may suffer significant changes in a few minutes;
• logistics for an adequate sampling are expensive and time consuming;
• a real need for quasi-real time data for making decisions.

• Sampling and transmission of data: analogical and digital circuits are responsible for commanding the sensor array, engineering variables and activate the satellite transmitter;
• Sampling: in each hour a new set of data are stored in a memory buffer;
• Transmission scheme: in each 90 seconds, one of eight buffers is transmitted through a carousel scheme. The transmission is performed independent of existing satellite to receive data;
• Reception of data: the INPE's units in Cuiabá (Mato Grosso State) and Alcântara (Maranhão State) received the data from satellites and then transmit to the unit in Nata (Rio Grande do Norte State); where the data are processed to filter the gaps in the transmission and to send to office (Remote Sensing Division) in São José dos Campos, São Paulo State. At office, the data are decoded, processed and stored;
• Data distribution: the web page is used to query and to visualized (through tables and graphs) all available data;
• SIMA self storage: some SIMAs buoy have the capacity of store the data to posterior download (this data are not transmitted by satellite). In this case, the samples are taken every 10 minutes.

The SIMA buoy collects some environmental variables from sensors above water (air temperature, atmospheric pressure, wind direction and velocity, incident and reflected shortwave radiation) and bellow water (ammonia, nitrate, chlorophyll-a, electric conductivity, water direction and velocity, dissolved oxygen, pH and water temperature in different depths).

SIMA was developed in partnership between the Vale do Paraíba University and the National Institute of Space Research. Since 1995, the project was transferred to a private enterprise (Neuron Engenharia LTDA). In association with Directorate of Hydrography and Navigation of Brazil, Neuron built a prototype of SIMA, where was anchored in the coastal zone of Rio de Janeiro state during a year. The collected data during this experiment were compared with in situ collected data, which confirmed the good performance of the system.

• The main observed problem are divided into sensors and satellite. The sensors problems is due to the environmental characteristics of each water body. In acid waters the sensors of water quality rapidly degrade, and the collected data are invalid. Another problem is the infestation of periphyton in the sensor.
• SIMA buoy makes the parameters readings every hour, or 24 readings per day. However, not always received all readings because the system requires satellites passing over the buoy antenna to complete the transfer and due to the satellite constellation position, some locations inland are not met as often as necessary to complete all transmissions. This is the more often causes for lack in the time series.