diff --git a/src/instrument/instrument_transforms.jl b/src/instrument/instrument_transforms.jl
index 917ea58cd..130fe002a 100644
--- a/src/instrument/instrument_transforms.jl
+++ b/src/instrument/instrument_transforms.jl
@@ -35,7 +35,7 @@ struct InstrumentTransform{T, L <: SiteLookup} <: AbstractInstrumentTransform
     site_map::L
 end
 
-function TV.inverse_eltype(::AbstractInstrumentTransform, x)
+function TV.inverse_eltype(::AbstractInstrumentTransform, x::Type)
     return eltype(x)
 end
 
diff --git a/src/instrument/priors/array_priors.jl b/src/instrument/priors/array_priors.jl
index 9c49dda39..c2e91d08a 100644
--- a/src/instrument/priors/array_priors.jl
+++ b/src/instrument/priors/array_priors.jl
@@ -42,15 +42,15 @@ end
 # end
 
 
-struct ObservedArrayPrior{D, S} <: Distributions.ContinuousMultivariateDistribution
-    dists::D
+struct ObservedArrayPrior{D, DS, S} <: Distributions.ContinuousMultivariateDistribution
+    sitedists::DS
     sitemap::S
-    phase::Bool
 end
 Base.eltype(d::ObservedArrayPrior) = eltype(d.dists)
 Base.length(d::ObservedArrayPrior) = length(d.dists)
 Dists._logpdf(d::ObservedArrayPrior, x::AbstractArray{<:Real}) = Dists._logpdf(d.dists, parent(x))
 Dists._rand!(rng::Random.AbstractRNG, d::ObservedArrayPrior, x::AbstractArray{<:Real}) = SiteArray(Dists._rand!(rng, d.dists, x), d.sitemap)
+
 function asflat(d::ObservedArrayPrior)
     d.phase && MarkovInstrumentTransform(asflat(d.dists), d.sitemap)
     return InstrumentTransform(asflat(d.dists), d.sitemap)
@@ -197,7 +197,7 @@ HypercubeTransform.ascube(t::PartiallyConditionedDist) = PartiallyFixedTransform
 function build_dist(dists::NamedTuple, smap::SiteLookup, array, refants, centroid_station)
     ts = smap.times
     ss = smap.sites
-    # fs = smap.frequencies
+    fs = smap.frequencies
     fixedinds, vals = reference_indices(array, smap, refants)
 
     if !(centroid_station isa Nothing)
@@ -212,9 +212,22 @@ function build_dist(dists::NamedTuple, smap::SiteLookup, array, refants, centroi
 
     variateinds = setdiff(eachindex(ts), fixedinds)
     dist = map(variateinds) do i
-        getproperty(dists, ss[i]).dist
+        s = ss[i]
+        sitedist(getproperty(dists, s), s, ts[i], fs[i], smap)
     end
     dist = Dists.product_distribution(dist)
     length(fixedinds) == 0 && return dist
     return PartiallyConditionedDist(dist, variateinds, fixedinds, vals)
 end
+
+function sitedist(dist::IIDSitePrior, site, time, freq, smap)
+    return dist.dist
+end
+
+function sitedist(dist::RWSitePrior, site, time, freq, smap)
+    if time > first(smap.times[smap.lookup[site]])
+        return dist.trans
+    else
+        return dist.dist0
+    end
+end
diff --git a/src/instrument/priors/independent.jl b/src/instrument/priors/independent.jl
index 1c7501576..37fb84ca0 100644
--- a/src/instrument/priors/independent.jl
+++ b/src/instrument/priors/independent.jl
@@ -1,7 +1,22 @@
-export IIDSitePrior
+export IIDSitePrior, RWSitePrior
 
+"""
+    AbstractSitePrior
+
+An abstract type for site priors. This defines an abstract distribution for the prior of a single
+site (antenna). Specific site priors should subtype this abstract type and then implement 
+```julia
+sitedist(d::AbstractSitePrior, site::Symbol, time, frequency, sitemap::SiteMap)
+```
+"""
 abstract type AbstractSitePrior end
 
+"""
+    sitedist(d::AbstractSitePrior, site::Symbol, time, frequency, smap)
+Get the distribution for a specific site at a specific time and frequency,
+"""
+function sitedist end
+
 segmentation(d::AbstractSitePrior) = getfield(d, :seg)
 
 """
@@ -24,3 +39,29 @@ struct IIDSitePrior{S <: Segmentation, D} <: AbstractSitePrior
     seg::S
     dist::D
 end
+
+"""
+    RWSitePrior(seg::Segmentation, dist0, transition)
+
+Create a site prior that is essentially a random walk from segment to segment.
+The `seg` argument is a segmentation object that defines how fine the time
+segmentation is. The `dist0` argument is the distribution for the initial scan,
+and the `transition` argument is the distribution for the transition between segments.
+
+This means
+x0 ~ dist0
+xt = x0 + ϵt,  where ϵt ~ transition
+
+
+## Example
+
+```julia
+A = RWSitePrior(ScanSeg(),  Normal(0, 1), Normal(0, 0.1))
+```
+
+"""
+struct RWSitePrior{S <: Segmentation, D0, DT} <: AbstractSitePrior
+    seg::S
+    dist0::D0
+    trans::DT
+end
diff --git a/src/instrument/site_array.jl b/src/instrument/site_array.jl
index 909ed2506..4729612b2 100644
--- a/src/instrument/site_array.jl
+++ b/src/instrument/site_array.jl
@@ -152,10 +152,14 @@ sites(s::SiteLookup) = s.sites
 frequencies(s::SiteLookup) = s.frequencies
 lookup(s::SiteLookup) = s.lookup
 
-EnzymeRules.inactive(::typeof(times), ::SiteLookup) = nothing
-EnzymeRules.inactive(::typeof(frequencies), ::SiteLookup) = nothing
-EnzymeRules.inactive(::typeof(sites), ::SiteLookup) = nothing
-EnzymeRules.inactive(::typeof(lookup), ::SiteLookup) = nothing
+times(s::SiteLookup, site::Symbol) = view(times(s), lookup(s)[site])
+frequencies(s::SiteLookup, site::Symbol) = view(frequencies(s), lookup(s)[site])
+sites(s::SiteLookup, site::Symbol) = view(sites(s), lookup(s)[site])
+
+EnzymeRules.inactive(::typeof(times), ::SiteLookup, ::Any...) = nothing
+EnzymeRules.inactive(::typeof(frequencies), ::SiteLookup, ::Any...) = nothing
+EnzymeRules.inactive(::typeof(sites), ::SiteLookup, ::Any...) = nothing
+EnzymeRules.inactive(::typeof(lookup), ::SiteLookup, ::Any...) = nothing
 
 function sitemap!(f, out::AbstractArray, gains::AbstractArray, slook::SiteLookup)
     return map(lookup(slook)) do site