Hi everyone,

Quick question on the units used for the ouput of r.sun in mode 2 (daily

sums):

In the manual pages for r.sun, the following 'unit' is included in the

description:

----------------------------

The solar radiation maps for given day are computed integrating the relevant

irradiance between sunrise and sunset times for given day. The user can set

finer or coarser time step step used for all-day radiation calculations. A

default value of step is 0.5 hour. Larger steps (e.g. 1.0-2.0) can speed-up

calculations but produce less reliable results. The output units are in Wh

per squared meter per given day [Wh/(m*m)/day].

-------------------------

Is one to interpret this as "watt-hour per square meter per day" ?

This would seem a little odd, as the the unit 'watt-hour' is not an SI unit.

Hopefully I am reading this incorectly.

An alternative interpretation of these units (one which I hope to be the

correct one):

Wh.m-2.day-1 = "watts per square meter per day, as estimated at some fraction

of an hour" ?

Any thoughts would be appreciated,

Dylan

--

Dylan Beaudette

Soils and Biogeochemistry Graduate Group

University of California at Davis

530.754.7341

Dylan Beaudette wrote:

Quick question on the units used for the ouput of r.sun in mode 2 (daily

sums):

In the manual pages for r.sun, the following 'unit' is included in the

description:

----------------------------

The solar radiation maps for given day are computed integrating the relevant

irradiance between sunrise and sunset times for given day. The user can set

finer or coarser time step step used for all-day radiation calculations. A

default value of step is 0.5 hour. Larger steps (e.g. 1.0-2.0) can speed-up

calculations but produce less reliable results. The output units are in Wh

per squared meter per given day [Wh/(m*m)/day].

-------------------------

Is one to interpret this as "watt-hour per square meter per day" ?

This would seem a little odd, as the the unit 'watt-hour' is not an SI unit.

More odd (to me) is having (different) units of time in both the

numerator and denominator. I would have thought it more logical to

divide the result by 24 to give Watts per square metre [W/(m^2)].

--

Glynn Clements <glynn@gclements.plus.com>

On Wednesday 29 November 2006 12:31, Glynn Clements wrote:

Dylan Beaudette wrote:

> Quick question on the units used for the ouput of r.sun in mode 2 (daily

> sums):

>

> In the manual pages for r.sun, the following 'unit' is included in the

> description:

> ----------------------------

> The solar radiation maps for given day are computed integrating the

> relevant irradiance between sunrise and sunset times for given day. The

> user can set finer or coarser time step step used for all-day radiation

> calculations. A default value of step is 0.5 hour. Larger steps (e.g.

> 1.0-2.0) can speed-up calculations but produce less reliable results. The

> output units are in Wh per squared meter per given day [Wh/(m*m)/day].

> -------------------------

>

> Is one to interpret this as "watt-hour per square meter per day" ?

> This would seem a little odd, as the the unit 'watt-hour' is not an SI

> unit.

More odd (to me) is having (different) units of time in both the

numerator and denominator. I would have thought it more logical to

divide the result by 24 to give Watts per square metre [W/(m^2)].

I need to check with some local experts, but judging from some recent tests -

the output from r.sun is comparible to that from a weather station, with

*hourly* averaged data in W/(m^2) which i think is analogous to the Wh/(m^2)

units that r.sun uses.

--

Dylan Beaudette

Soils and Biogeochemistry Graduate Group

University of California at Davis

530.754.7341