Hi Andreas,

First of all, it is a very thorough question indeed...

I am keenly following the biomass estimation recently for my research. There have been enormous efforts in this domain. However, I have seen many of them were concentrating on the estimation per se. If we have a look further that many disagreement exist between the use of local and regional allometric equations, I believe this is important as this would be the "ground truth" data where remote sensing data need to be correlated. Due to the disgreement, at least in my case, "ground truth AGB" can be widely varied. So I would suggest to see the AGB data on the first instance, before elaborating remote sensing data. If possible, I think it is also useful to see the allometric equation and its bounds. With my ground data, for instance, I've got AGB using Chave's equation almost 150% more than the one given by Ketterings, while the latter is a bit consistent to rubber-specific equation derived from Indonesian site. Interestingly, Thailand-based equation is nicely comparable to Chave than Ketterings.

I do not work with steppe, but with plantations. It looks that steppe biomass would be comparable to young rubber plantation. I found that the relationship was severely low between fairly dense reeds and P-and L-band SAR, hence in my case C-band is advisable.

HTH, Bambang

thank you, Bambang and Waqas, for your contributions! I will have a look at the distribution of my ground truth data and also search for the suggested work in Sudan.

I will share my findings here, if you are interested.

Let me answer my own question: I integrated active and passive radar imagery in an semi-arid ecosystem with biomass values below 10 t/ha. I found that combining ALOS, ENVISAT and SSM/I is able to predict biomass at this scale, as long as it remains within a smaller range.

Maybe this is interesting to some of you, Bambang H Trisasongko , Waqas Qazi or anyone who stumbles upon this question.

Article Above-ground biomass estimates based on active and passive m...

Nasir Hameed Thank you for your interest. I infer that current wide-swath SAR (e.g. Sentinel-1 or ALOS-2) can predict above-ground biomass also in low-biomass regions, especially when combined with brightness temperature (e.g. by Sentinel-3 or SSMI/I). However, the quality of the predictions strongly depend from the availability of field measurements which are systematically acquired over longer times.

Also the relationship between the sampling area and the spatial resolution of the sensors (100-250 m seems feasible for large-scale studies) is crucial.

We reached R² of up to 0.52 which is the highest I currently know for these kind of savanna ecosystems. If you find similar studies, please let me know, or simply share in here.

I also found that the article I linked above is now at a different location: https://www.researchgate.net/publication/329582330_Above-ground_biomass_estimates_based_on_active_and_passive_microwave_sensor_imagery_in_low-biomass_savanna_ecosystems