It would be good to have satellites that gave current readings of skin temperature so that farmers could see if their crop was freezing or too hot, as well as for other global warming monitoring. Would this be possible, why isn't there one?
It would be good to have satellites that gave current readings of skin temperature so that farmers could see if their crop was freezing or too hot
This is not generally possible in near real time ("live update"), but satellites may still offer some useful information. There are several problems:
- Satellites can measure skin temperature using infrared sensors only in the absence of clouds. On average, 67% of Earth and 55% of land is covered in clouds (King et. al, 2013) (of course, this number various strongly with time and place). Therefore, much or most of the time, satellites cannot measure skin temperature instantly, but have to wait for a cloud-free moment. However, dry nights (no cloud and not much water vapour) cool down more than humid or cloudy nights, so maybe during the most at-risk nights the radiometres can still give a clue.
- To monitor in near-real time, you need to use either geostationary satellites or a very large swarm of low Earth Orbit satellites.
- The spatial resolution of infrared channels in geostationary satellites is too poor. Most geostationary imagers have resolutions of more than a kilometre. The current Meteosat generation has 3×3 km² at sub satellite point and closer to 4×6 km² in central Europe.
- A very large swarm would be costly, and the infrared resolution would still be dozens of metres.
- High resolution imagers in any case only regard a small area at any time.
- In theory, microwave can be used to measure surface temperature in the presence of clouds (although for a thicker layer than infrared), but only with a good knowledge of surface emissivity (which is a function of soil moisture, among other things), and the spatial resolution of microwave sensors is much worse (>10 km from low earth orbit, non-existent from geostationary orbit).
A resolution of 1×1 km² from geostationary orbit would already be very ambitious, where 2×2 km² or more is more realistic. I'm not sure if this is good enough for farmers for discriminating the skin temperature of their crops from the skin temperature of the general area, which may be quite different (heat loss in a clear night strongly depends on surface material).
Farmers who wish to monitor their crop temperature in real time should probably just use infrared cameras installed at their property or possibly with drones constantly flying in the air. Whether this is cost-effective is beyond the scope of Earth Science SE.
as well as for other global warming monitoring
This is routinely done, but this does not need a high spatial resolution and it does not need to be in near real time.
M. D. King, S. Platnick, W. P. Menzel, S. A. Ackerman and P. A. Hubanks, "Spatial and Temporal Distribution of Clouds Observed by MODIS Onboard the Terra and Aqua Satellites," in IEEE Transactions on Geoscience and Remote Sensing, vol. 51, no. 7, pp. 3826-3852, July 2013, doi: 10.1109/TGRS.2012.2227333. Accessed online 5 April 2022.
Not, because the costs of satellite image provider are excessive, and the same idea can be exploited with drones (and in fact it is being commercially exploited, as it can be seen by accessing this report https://www.businessinsider.com/agricultural-drones-precision-mapping-spraying?r=US&IR=T ).
I suggest to have a look at this study: https://www.researchgate.net/publication/341253627_Applications_of_UAV_Thermal_Imagery_in_Precision_Agriculture_State_of_the_Art_and_Future_Research_Outlook to understand where we are in 2022 in terms of implementation of remote sensing and precision agriculture (we are quite ahead wrt to what OP question implies).