Previous entries: Before July 97.
Jeffrey West
The following comments address the needs of the Forest Mapping Work Group. They are based on discussions with a few of the work group members and may not be inclusive
General Work Group Data Needs:
Wet deposition
The most recent five-year average should be reported for deposition chemistry. The mandatory parameters for deposition chemistry are:
Area-wide gridded compilations of all major ions (as noted above) are required. To start the process long term average numbers are fine. An annual summary of the last 20 years by grid cell would be useful. Point data from the various monitoring sties is also required
Dry deposition:
Dry deposition is required by the forest mapping work group for input into the Simple Mass Balance model. Any estimates that can be supplied by the Data Exchange group would be appreciated. We are ourselves are currently looking into a multiplier based on current scientific knowledge. We will share anything we come up with.
Fog deposition:
Fog deposition can play a significant role especially in the mountainous New England states. A geospatial model for the NE States has been developed by Eric Miller at Dartmouth College in Hanover NH. We are looking into the possibility of expanding the model to the Eastern Provinces in Canada.
Data Format Issues:
We will be using ArcInfo/ArcView for the forest mapping project. We would like to get a raster (gridded) coverage from the NatChem database to test the ease to which the coverage can be imported into ArcInfo. As for the grid size, based on the scale of the data we are working with a finer resolution would be preferable (even 10-20km). However, if the spacing of the monitoring sites makes this resolution artificial than there is no sense going finer than 40km.
With respect to projection, my initial thought is that we agree to work in decimal degrees (no projection). This will allow us the flexibility in ArcView of projecting the data into whatever projection we want for display purposes.
Future Steps
A spatio-temporal model that shows how deposition changes by area and time.
Dry deposition needs to be addressed sooner than later. I would suggest that this item come off the "back burner".
Data Needs
I think that Rich has identified the appropriate list of data needs, but would like to add a vote for also including the measured wet deposition concentration and precipitation volume data, i.e. the data underlying the spatial grids. These data would be useful for trend analyses, input into alternative spatial interpolation techniques and verification of models and regridded maps. Also, where possible, provide the raw data at a daily or weekly time step. Having the finer temporal resolution would enable one to perform episode analyses and source attribution studies.
Data Format: Grid Compatibility Issue
Obtaining gridded versions of the NAtChem maps and regidding these and/or other maps for comparison is a logical solution to the format conflict. To minimize any distortion and information loss in the regridding one would want as fine a grid as possible. So is the 40km grid fine enough? This depends on the monitoring site density and the spatial variability in the monthly data. As far as station density goes, 84% of the US NADP sites, east of the Mississippi, have the closest neighboring site 40 km or more away with an average distance of about 100 km. Unless the spatial data is very heterogeneous I would think that a 40 km grid is probably adequate.
Future Steps: Dry Deposition Estimates
The CASTNet network has about 45 sites throughout the Eastern US collecting data suitable for dry deposition estimates, and a number of people have published dry deposition estimates based upon these data. No matter how "non-representative" these CASTNet sites maybe to the neighboring non monitored area, spatial interpolating these data would have to provide a better estimate than simply assuming Dry = Wet. At a minimum the Dry/Wet ratio could be calculated at each CASTNet site which in conjunction with the wet deposition data could be used to estimate spatial patterns of dry deposition.
First of all, I am willing to participate in a small Data Formats discussion group or a GIS related discussion group. I do have extended expertise...