MSL Rover Environmental Monitoring Station (REMS)

Except where indicated in red or blue, this article was originally written by Javier Gomez-Elvira, Centrol de Astrobiologia, Spain. One of the two wind booms shown below failed on landing. 

REMS has been designed to record six atmospheric parameters: wind speed/direction, pressure, relative humidity, air temperature, ground temperature, and ultraviolet radiation. All sensors are located around three elements: two booms attached to the rover Remote Sensing Mast (RSM), the Ultraviolet Sensor (UVS) assembly located on the rover top deck, and the Instrument Control Unit (ICU) inside the rover body.

The booms are approximately 1.5 m above ground level. Boom length is similar to the RSM diameter, and therefore the wind flow perturbation by the RSM may reach the boom tip where the wind sensor is located. The two booms are separated in azimuth by 120 degrees to help insure that at least one of them will record clean wind data for any given wind direction. The figure below shows the booms’ relative position. There is a 50 mm height difference to minimize mutual wind perturbation.

Boom 2, which points in the driving direction of the rover, has wind sensors and the relative humidity sensor. As of May 24, 2017 REMS has failed to include a single relative humidity figure on its daily weather reports to the public. You can track what they have to date at our MSL Weather Record page. At REMS Reports we show how many simple errors REMS has made in their public weather reports.  Promises of more significant weather reports at NASA's PDS site went unfulfilled for at least a year. When we asked another physicist to check on what was eventually largely hidden from the public. He first said he found temperature increases between 1.75 meters above ground level and 2 meters of 20 to 30 degrees Celsius, but then realized that he was looking at Phoenix temperatures.  He said it's almost impossible to decipher the site and that this was likely deliberate. On the belief that NASA sees the Roffman Team as hostile, I asked him to call the owners of the data and get clarification. He then sent me extensive data for Phoenix with columns headed as follows: (1) Time every 2 seconds with time zero =13 hours 19 minutes  57 seconds True local solar time on Mars, (2) Pressure in Pa, (3) Temp K @ 0.5 m, (4) Temp K @ 1 m, (5) Temp K @ 1.5 m, and (6) Temp K @ 2 m. What's wrong with this data? There are 4 altitudes for temperatures but only three altitudes on Phoenix where temperatures could be taken. For a discussion of the three Phoenix sensors, please read the following extract of an article by Peter A. Taylor Et Al., 2008):

2.1 Temperature Measurements. Air temperatures and temperature differences between levels will be monitored, almost continuously, by three temperature sensors based on fine wire, butt-welded thermocouples (75 µm diameter, Constantan-Chromel) mounted in C frames on a 1 m mast, coupled with a reference platinum resistance thermometer (PRT) in an isothermal block containing the ‘‘cold’’ junctions of the thermocouples. Levels on the mast are 0.25, 0.5, and 1.0 m above the lander deck, which itself is ~1 m above the ground.

Boom 1, which looks to the side and slightly to the rear of the rover, hosts another set of wind sensors and the ground temperature sensor. Both booms have an air temperature sensor. Boom 1 was reported broken after the landing. Winds were reported stuck every day at 2 m/s (7.2 km/h) from the east ever since REMS began to issue daily weather reports until May 2013 when we made an issue of it to Guy Webster, a NASA/JPL public affairs manager. There was no working ability to tell either the real wind speed or direction. As of today, there is reason to question all weather data.  From September 1, 2012 until September 5, 2012, REMS reported pressures of 742 to 747 hPa (mbar), then dropped back to 7.47 Pa  (7.47 hPa) the next day. On 10/17/2012 they provided no pressure, just a temperature for Sol 68 10/13/2012, and on 10/18/2012 they offered a pressure for Sol 70 on 10/16/2012, but seemed to lose Sol 69 and all data for October 14-15. This pattern of lost and mislabed Sols continued into 2013. Eventually I saw the need to start a separate record just devoted to sol numbering problems. It is located HERE. For a summary all of the weather reporting problems see our PowerPoint.

Wind speed and direction will be derived based on information provided by three two-dimensional wind sensors on each of the booms. The three sensors are located 120 degrees apart around the boom axis. Each of them will record local speed and direction in the plane of the sensor. The convolution of the 12 data points will be enough to determine wind speed as well as pitch and yaw angle of each boom relative to the flow direction. The requirement is to determine horizontal wind speed with 1 m/sec accuracy in the range of 0 to 70 m/sec, with a resolution of 0.5 m/sec. The directional accuracy is expected to be better than 30 degrees. For vertical wind the range is 0 to 10 m/sec, and the accuracy and resolution are the same as for horizontal wind.

As mentioned previously, the wind field at the booms will be perturbed by the RSM and by the rover itself. Calibration will be done via a variety of wind tunnel tests under Mars conditions as well as numerical analysis. Simulations will be used to obtain results where tests conditions cannot be reproduced on Earth.

Ground temperature will be recorded with a thermopile on Boom 1 that views the Martian surface to the side of the rover through a filter with a passband of 8 to 14 microns. The requirement is to measure ground brightness temperature over the range from 150 to 300 K with a resolution of 2 K and an accuracy of 10 K.

Air temperature will be recorded at both booms with a PT1000-type sensor placed on a small rod long enough to be outside the mast and boom thermal boundary layers. Its measurement range is 150 to 300 K. It has an accuracy of 5 K and a resolution of 0.1 K.

Boom 2 houses the humidity sensor, which is located inside a protective cylinder. That sensor will measure relative humidity with an accuracy of 10% in the 200-323 K range and with a resolution of 1%. A dust filter protects it from dust deposition. We believe that the tiny dust filter design on the FMI Vaisala pressure transducer (similar to that flown on the Phoenix) is fatally flawed. There is no ability to change it when it becomes clogged. We are not sure if a similar problem with the dust filter for the humidity sensor is what is keeping REMS from reported any data for relative humidity on its daily reports. We discussed the pressure sensor dust filter problem twice with Dr. Ashwin Vasavada at JPL before MSL was launched. UPDATE OF 8 March 2016: The REMS  team was published two pressures that are above the 1150 Pa limit. They are 1177 Pa for Sol 1160 and 1200 Pa for Sol 1161. See the print screen for these reports here. However, after we made an issue of these pressures that were higher than the 1150 Pa maximum ability of the Vaisala sensor, REMS dropped the values back to 898 and 899 Pa - see http://davidaroffman.com/images/1160_and_1161_changes.png. REMS often altered pressures after we highlighted problematic ones. Some examples follow in Table 1 below:

Table 1 shows some (not all) of how JPL/REMS altered off the curve data for August and September 2012 and August 2013 and on through at least March 4, 2017 after we either brought the deviations up to JPL Public Relations Director Guy Webster, or published them on our davidaroffman.com and marscorrect.com websites.

Two of the main constraints on the REMS instrument design are the need for the booms to survive and operate in a broad range of temperatures, and for the entire instrument to have a mass less than 1.3 kg. Both conditions have required the development of an ASIC for data conditioning which must survive a -130 °C to +70 °C temperature range and minimize power consumption for operation.

The UV sensor will be located on the rover deck and is composed of six photodiodes in the following ranges: 315-370 nm (UVA), 280-320 nm (UVB), 220-280 nm (UVC), 200-370 nm (total dose), 230-290 nm (UVD), and 300-350 nm (UVE), with an accuracy better than 8% of the full range for each channel, computed based on Mars radiation levels and minimum dust opacity. The photodiodes face the zenith direction and have a field of view of 60 degrees. The sensor will be placed on the rover deck without any dust protection. To mitigate dust degradation, a magnetic ring has been placed around each photodiode with the aim of maximizing their operational time. Nevertheless, to evaluate dust deposition degradation, images of the sensor will be recorded periodically. Comparison of these images with laboratory measurements will permit evaluation of the level of dust absorption.

The pressure sensor will be located inside the rover body and connected to the external atmosphere via a tube. The tube exits the rover body through a small opening with protection against dust deposition. Its measurement range goes from 1 to 1150 Pa with an end-of-life accuracy of 20 Pa (calibration tests give values around 3 Pa) and a resolution of 0.5 Pa. As this component will be in contact with the atmosphere, a HEPA filter will be placed on the tube inlet to avoid contaminating the Mars environment. Note: 1150 Pa is only 11.5 mbar. This max pressure allowed is far too low to account for dust storms and other weather plainly seen on Mars. It is evidence that this Vaisala instrument is fatally flawed in its conception. See our page on the Phoenix Vaisala and especially our page about Sol 370 when an initial mean pressure of 1149 Pa was published (though later altered to 865 Pa after we raised an issued about it).

Systematic measurement is the main driver for REMS operation. Each hour, every sol, REMS will record 5 minutes of data at 1 Hz for all sensors. This strategy will be implemented based on a high degree of autonomy in REMS operations. The instrument will wake itself up each hour and after recording and storing data, will go to sleep independently of rover operations. REMS will record data whether the rover is awake or not, and both day and night. It is expected that under certain conditions, the ground temperature and humidity sensor measurements will require the integration of multiple measurement samples within the 5-minute interval in order to meet their science requirements.

REMS operation is designed assuming an integrated total of three hours of operation each day, primarily constrained by power availability. Nevertheless, the REMS science team will have the capability to define additional prescheduled observation periods with durations longer than 5 minutes and located at any time during the day. Since the hourly observations will use a total of two hours of operational time, the third hour can be scheduled as a continuous block, for example. Another option that has been implemented in REMS flight software is a simple algorithm to lengthen some of the regular observations autonomously when an atmospheric event is detected.

The main science objectives that the science team will focus on are:

• Signature of the Martian general circulation and mesoscale phenomena near the surface (e.g., fronts, jets). NOTE: Fronts can be distinguished by noticeable changes in temperature, pressure, and by the presence of clouds. However, as we prove with before and after print-screens on our REMS weather report spreadsheets, when we note significant changes in pressure (see Table 1 above) and temperature, the REMS Team and/or their superiors at in Madrid (Consejo Superior de Investigaciones, on line with IP address 161.111.124.7 or at JPL alter their data - effectively wiping out evidence of the front. Likewise, as of at least this date, none of the 1,661 sols at MSL have been reported as anything but sunny. These changes are folly documented as of today at the links below:

• Microscale weather systems (e.g., boundary layer turbulence, heat fluxes, dust devils)

• Local hydrological cycle (e.g., spatial and temporal variability, diffusive transport from regolith)

• Destructive potential of UV radiation, dust UV optical properties, photolysis rates, and oxidant production. HOWEVER, all low ultraviolet radiation reports have been eliminated by the REMS Team or their superiors.

• Subsurface habitability based on ground-atmosphere interaction

Figure 2 below: Early ground and air temperatures claimed by the REMS Team for MSL sols 10 and 11.